sys_vars.cc

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/* Copyright (c) 2009, 2013, Oracle and/or its affiliates. All rights reserved.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

#include "my_global.h"                          /* NO_EMBEDDED_ACCESS_CHECKS */
#include "sql_priv.h"
#include "sql_class.h"                          // set_var.h: THD
#include "rpl_gtid.h"
#include "sys_vars.h"
#include "mysql_com.h"

#include "events.h"
#include <thr_alarm.h>
#include "rpl_slave.h"
#include "rpl_mi.h"
#include "rpl_rli.h"
#include "rpl_slave.h"
#include "rpl_info_factory.h"
#include "transaction.h"
#include "opt_trace.h"
#include "mysqld.h"
#include "lock.h"
#include "sql_time.h"                       // known_date_time_formats
#include "sql_acl.h" // SUPER_ACL,
                     // mysql_user_table_is_in_short_password_format
                     // disconnect_on_expired_password
#include "derror.h"  // read_texts
#include "sql_base.h"                           // close_cached_tables
#include "debug_sync.h"                         // DEBUG_SYNC
#include "hostname.h"                           // host_cache_size
#include "sql_show.h"                           // opt_ignore_db_dirs
#include "table_cache.h"                        // Table_cache_manager

#include "log_event.h"
#ifdef WITH_PERFSCHEMA_STORAGE_ENGINE
#include "../storage/perfschema/pfs_server.h"
#endif /* WITH_PERFSCHEMA_STORAGE_ENGINE */

TYPELIB bool_typelib={ array_elements(bool_values)-1, "", bool_values, 0 };

/*
  This forward declaration is needed because including sql_base.h
  causes further includes.  [TODO] Eliminate this forward declaration
  and include a file with the prototype instead.
*/
extern void close_thread_tables(THD *thd);


static bool update_buffer_size(THD *thd, KEY_CACHE *key_cache,
                               ptrdiff_t offset, ulonglong new_value)
{
  bool error= false;
  DBUG_ASSERT(offset == offsetof(KEY_CACHE, param_buff_size));

  if (new_value == 0)
  {
    if (key_cache == dflt_key_cache)
    {
      my_error(ER_WARN_CANT_DROP_DEFAULT_KEYCACHE, MYF(0));
      return true;
    }

    if (key_cache->key_cache_inited)            // If initied
    {
      /*
        Move tables using this key cache to the default key cache
        and clear the old key cache.
      */
      key_cache->in_init= 1;
      mysql_mutex_unlock(&LOCK_global_system_variables);
      key_cache->param_buff_size= 0;
      ha_resize_key_cache(key_cache);
      ha_change_key_cache(key_cache, dflt_key_cache);
      /*
        We don't delete the key cache as some running threads my still be in
        the key cache code with a pointer to the deleted (empty) key cache
      */
      mysql_mutex_lock(&LOCK_global_system_variables);
      key_cache->in_init= 0;
    }
    return error;
  }

  key_cache->param_buff_size= new_value;

  /* If key cache didn't exist initialize it, else resize it */
  key_cache->in_init= 1;
  mysql_mutex_unlock(&LOCK_global_system_variables);

  if (!key_cache->key_cache_inited)
    error= ha_init_key_cache(0, key_cache);
  else
    error= ha_resize_key_cache(key_cache);

  mysql_mutex_lock(&LOCK_global_system_variables);
  key_cache->in_init= 0;

  return error;
}

static bool update_keycache_param(THD *thd, KEY_CACHE *key_cache,
                                  ptrdiff_t offset, ulonglong new_value)
{
  bool error= false;
  DBUG_ASSERT(offset != offsetof(KEY_CACHE, param_buff_size));

  keycache_var(key_cache, offset)= new_value;

  key_cache->in_init= 1;
  mysql_mutex_unlock(&LOCK_global_system_variables);
  error= ha_resize_key_cache(key_cache);

  mysql_mutex_lock(&LOCK_global_system_variables);
  key_cache->in_init= 0;

  return error;
}

/*
  The rule for this file: everything should be 'static'. When a sys_var
  variable or a function from this file is - in very rare cases - needed
  elsewhere it should be explicitly declared 'export' here to show that it's
  not a mistakenly forgotten 'static' keyword.
*/
#define export /* not static */

#ifdef WITH_PERFSCHEMA_STORAGE_ENGINE
#ifndef EMBEDDED_LIBRARY

#define PFS_TRAILING_PROPERTIES \
  NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(NULL), ON_UPDATE(NULL), \
  NULL, sys_var::PARSE_EARLY

static Sys_var_mybool Sys_pfs_enabled(
       "performance_schema",
       "Enable the performance schema.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_enabled),
       CMD_LINE(OPT_ARG), DEFAULT(TRUE),
       PFS_TRAILING_PROPERTIES);

static Sys_var_charptr Sys_pfs_instrument(
       "performance_schema_instrument",
       "Default startup value for a performance schema instrument.",
       READ_ONLY NOT_VISIBLE GLOBAL_VAR(pfs_param.m_pfs_instrument),
       CMD_LINE(OPT_ARG, OPT_PFS_INSTRUMENT),
       IN_FS_CHARSET,
       DEFAULT(""),
       PFS_TRAILING_PROPERTIES);

static Sys_var_mybool Sys_pfs_consumer_events_stages_current(
       "performance_schema_consumer_events_stages_current",
       "Default startup value for the events_stages_current consumer.",
       READ_ONLY NOT_VISIBLE GLOBAL_VAR(pfs_param.m_consumer_events_stages_current_enabled),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE),
       PFS_TRAILING_PROPERTIES);

static Sys_var_mybool Sys_pfs_consumer_events_stages_history(
       "performance_schema_consumer_events_stages_history",
       "Default startup value for the events_stages_history consumer.",
       READ_ONLY NOT_VISIBLE GLOBAL_VAR(pfs_param.m_consumer_events_stages_history_enabled),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE),
       PFS_TRAILING_PROPERTIES);

static Sys_var_mybool Sys_pfs_consumer_events_stages_history_long(
       "performance_schema_consumer_events_stages_history_long",
       "Default startup value for the events_stages_history_long consumer.",
       READ_ONLY NOT_VISIBLE GLOBAL_VAR(pfs_param.m_consumer_events_stages_history_long_enabled),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE),
       PFS_TRAILING_PROPERTIES);

static Sys_var_mybool Sys_pfs_consumer_events_statements_current(
       "performance_schema_consumer_events_statements_current",
       "Default startup value for the events_statements_current consumer.",
       READ_ONLY NOT_VISIBLE GLOBAL_VAR(pfs_param.m_consumer_events_statements_current_enabled),
       CMD_LINE(OPT_ARG), DEFAULT(TRUE),
       PFS_TRAILING_PROPERTIES);

static Sys_var_mybool Sys_pfs_consumer_events_statements_history(
       "performance_schema_consumer_events_statements_history",
       "Default startup value for the events_statements_history consumer.",
       READ_ONLY NOT_VISIBLE GLOBAL_VAR(pfs_param.m_consumer_events_statements_history_enabled),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE),
       PFS_TRAILING_PROPERTIES);

static Sys_var_mybool Sys_pfs_consumer_events_statements_history_long(
       "performance_schema_consumer_events_statements_history_long",
       "Default startup value for the events_statements_history_long consumer.",
       READ_ONLY NOT_VISIBLE GLOBAL_VAR(pfs_param.m_consumer_events_statements_history_long_enabled),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE),
       PFS_TRAILING_PROPERTIES);

static Sys_var_mybool Sys_pfs_consumer_events_waits_current(
       "performance_schema_consumer_events_waits_current",
       "Default startup value for the events_waits_current consumer.",
       READ_ONLY NOT_VISIBLE GLOBAL_VAR(pfs_param.m_consumer_events_waits_current_enabled),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE),
       PFS_TRAILING_PROPERTIES);

static Sys_var_mybool Sys_pfs_consumer_events_waits_history(
       "performance_schema_consumer_events_waits_history",
       "Default startup value for the events_waits_history consumer.",
       READ_ONLY NOT_VISIBLE GLOBAL_VAR(pfs_param.m_consumer_events_waits_history_enabled),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE),
       PFS_TRAILING_PROPERTIES);

static Sys_var_mybool Sys_pfs_consumer_events_waits_history_long(
       "performance_schema_consumer_events_waits_history_long",
       "Default startup value for the events_waits_history_long consumer.",
       READ_ONLY NOT_VISIBLE GLOBAL_VAR(pfs_param.m_consumer_events_waits_history_long_enabled),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE),
       PFS_TRAILING_PROPERTIES);

static Sys_var_mybool Sys_pfs_consumer_global_instrumentation(
       "performance_schema_consumer_global_instrumentation",
       "Default startup value for the global_instrumentation consumer.",
       READ_ONLY NOT_VISIBLE GLOBAL_VAR(pfs_param.m_consumer_global_instrumentation_enabled),
       CMD_LINE(OPT_ARG), DEFAULT(TRUE),
       PFS_TRAILING_PROPERTIES);

static Sys_var_mybool Sys_pfs_consumer_thread_instrumentation(
       "performance_schema_consumer_thread_instrumentation",
       "Default startup value for the thread_instrumentation consumer.",
       READ_ONLY NOT_VISIBLE GLOBAL_VAR(pfs_param.m_consumer_thread_instrumentation_enabled),
       CMD_LINE(OPT_ARG), DEFAULT(TRUE),
       PFS_TRAILING_PROPERTIES);

static Sys_var_mybool Sys_pfs_consumer_statement_digest(
       "performance_schema_consumer_statements_digest",
       "Default startup value for the statements_digest consumer.",
       READ_ONLY NOT_VISIBLE GLOBAL_VAR(pfs_param.m_consumer_statement_digest_enabled),
       CMD_LINE(OPT_ARG), DEFAULT(TRUE),
       PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_events_waits_history_long_size(
       "performance_schema_events_waits_history_long_size",
       "Number of rows in EVENTS_WAITS_HISTORY_LONG."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_events_waits_history_long_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024*1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_events_waits_history_size(
       "performance_schema_events_waits_history_size",
       "Number of rows per thread in EVENTS_WAITS_HISTORY."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_events_waits_history_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_ulong Sys_pfs_max_cond_classes(
       "performance_schema_max_cond_classes",
       "Maximum number of condition instruments.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_cond_class_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 256),
       DEFAULT(PFS_MAX_COND_CLASS),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_max_cond_instances(
       "performance_schema_max_cond_instances",
       "Maximum number of instrumented condition objects."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_cond_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024*1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_ulong Sys_pfs_max_file_classes(
       "performance_schema_max_file_classes",
       "Maximum number of file instruments.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_file_class_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 256),
       DEFAULT(PFS_MAX_FILE_CLASS),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_ulong Sys_pfs_max_file_handles(
       "performance_schema_max_file_handles",
       "Maximum number of opened instrumented files.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_file_handle_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 1024*1024),
       DEFAULT(PFS_MAX_FILE_HANDLE),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_max_file_instances(
       "performance_schema_max_file_instances",
       "Maximum number of instrumented files."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_file_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024*1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_max_sockets(
       "performance_schema_max_socket_instances",
       "Maximum number of opened instrumented sockets."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_socket_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024*1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_ulong Sys_pfs_max_socket_classes(
       "performance_schema_max_socket_classes",
       "Maximum number of socket instruments.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_socket_class_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 256),
       DEFAULT(PFS_MAX_SOCKET_CLASS),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_ulong Sys_pfs_max_mutex_classes(
       "performance_schema_max_mutex_classes",
       "Maximum number of mutex instruments.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_mutex_class_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 256),
       DEFAULT(PFS_MAX_MUTEX_CLASS),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_max_mutex_instances(
       "performance_schema_max_mutex_instances",
       "Maximum number of instrumented MUTEX objects."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_mutex_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 100*1024*1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_ulong Sys_pfs_max_rwlock_classes(
       "performance_schema_max_rwlock_classes",
       "Maximum number of rwlock instruments.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_rwlock_class_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 256),
       DEFAULT(PFS_MAX_RWLOCK_CLASS),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_max_rwlock_instances(
       "performance_schema_max_rwlock_instances",
       "Maximum number of instrumented RWLOCK objects."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_rwlock_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 100*1024*1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_max_table_handles(
       "performance_schema_max_table_handles",
       "Maximum number of opened instrumented tables."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_table_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024*1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_max_table_instances(
       "performance_schema_max_table_instances",
       "Maximum number of instrumented tables."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_table_share_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024*1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_ulong Sys_pfs_max_thread_classes(
       "performance_schema_max_thread_classes",
       "Maximum number of thread instruments.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_thread_class_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 256),
       DEFAULT(PFS_MAX_THREAD_CLASS),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_max_thread_instances(
       "performance_schema_max_thread_instances",
       "Maximum number of instrumented threads."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_thread_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024*1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_ulong Sys_pfs_setup_actors_size(
       "performance_schema_setup_actors_size",
       "Maximum number of rows in SETUP_ACTORS.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_setup_actor_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 1024),
       DEFAULT(PFS_MAX_SETUP_ACTOR),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_ulong Sys_pfs_setup_objects_size(
       "performance_schema_setup_objects_size",
       "Maximum number of rows in SETUP_OBJECTS.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_setup_object_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 1024*1024),
       DEFAULT(PFS_MAX_SETUP_OBJECT),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_accounts_size(
       "performance_schema_accounts_size",
       "Maximum number of instrumented user@host accounts."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_account_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024*1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_hosts_size(
       "performance_schema_hosts_size",
       "Maximum number of instrumented hosts."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_host_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024*1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_users_size(
       "performance_schema_users_size",
       "Maximum number of instrumented users."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_user_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024*1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_ulong Sys_pfs_max_stage_classes(
       "performance_schema_max_stage_classes",
       "Maximum number of stage instruments.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_stage_class_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 256),
       DEFAULT(PFS_MAX_STAGE_CLASS),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_events_stages_history_long_size(
       "performance_schema_events_stages_history_long_size",
       "Number of rows in EVENTS_STAGES_HISTORY_LONG."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_events_stages_history_long_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024*1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_events_stages_history_size(
       "performance_schema_events_stages_history_size",
       "Number of rows per thread in EVENTS_STAGES_HISTORY."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_events_stages_history_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_ulong Sys_pfs_max_statement_classes(
       "performance_schema_max_statement_classes",
       "Maximum number of statement instruments.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_statement_class_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 256),
       DEFAULT((ulong) SQLCOM_END + (ulong) COM_END + 4),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_events_statements_history_long_size(
       "performance_schema_events_statements_history_long_size",
       "Number of rows in EVENTS_STATEMENTS_HISTORY_LONG."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_events_statements_history_long_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024*1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_events_statements_history_size(
       "performance_schema_events_statements_history_size",
       "Number of rows per thread in EVENTS_STATEMENTS_HISTORY."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_events_statements_history_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_digest_size(
       "performance_schema_digests_size",
       "Size of the statement digest."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_digest_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024 * 1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

static Sys_var_long Sys_pfs_connect_attrs_size(
       "performance_schema_session_connect_attrs_size",
       "Size of session attribute string buffer per thread."
         " Use 0 to disable, -1 for automated sizing.",
       READ_ONLY GLOBAL_VAR(pfs_param.m_session_connect_attrs_sizing),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(-1, 1024 * 1024),
       DEFAULT(-1),
       BLOCK_SIZE(1), PFS_TRAILING_PROPERTIES);

#endif /* EMBEDDED_LIBRARY */
#endif /* WITH_PERFSCHEMA_STORAGE_ENGINE */

static Sys_var_ulong Sys_auto_increment_increment(
       "auto_increment_increment",
       "Auto-increment columns are incremented by this",
       SESSION_VAR(auto_increment_increment),
       CMD_LINE(OPT_ARG),
       VALID_RANGE(1, 65535), DEFAULT(1), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, IN_BINLOG);

static Sys_var_ulong Sys_auto_increment_offset(
       "auto_increment_offset",
       "Offset added to Auto-increment columns. Used when "
       "auto-increment-increment != 1",
       SESSION_VAR(auto_increment_offset),
       CMD_LINE(OPT_ARG),
       VALID_RANGE(1, 65535), DEFAULT(1), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, IN_BINLOG);

static Sys_var_mybool Sys_automatic_sp_privileges(
       "automatic_sp_privileges",
       "Creating and dropping stored procedures alters ACLs",
       GLOBAL_VAR(sp_automatic_privileges),
       CMD_LINE(OPT_ARG), DEFAULT(TRUE));

static Sys_var_ulong Sys_back_log(
       "back_log", "The number of outstanding connection requests "
       "MySQL can have. This comes into play when the main MySQL thread "
       "gets very many connection requests in a very short time",
       READ_ONLY GLOBAL_VAR(back_log), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 65535), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_charptr Sys_basedir(
       "basedir", "Path to installation directory. All paths are "
       "usually resolved relative to this",
       READ_ONLY GLOBAL_VAR(mysql_home_ptr), CMD_LINE(REQUIRED_ARG, 'b'),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_my_bind_addr(
       "bind_address", "IP address to bind to.",
       READ_ONLY GLOBAL_VAR(my_bind_addr_str), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(MY_BIND_ALL_ADDRESSES));

static bool fix_binlog_cache_size(sys_var *self, THD *thd, enum_var_type type)
{
  check_binlog_cache_size(thd);
  return false;
}

static bool fix_binlog_stmt_cache_size(sys_var *self, THD *thd, enum_var_type type)
{
  check_binlog_stmt_cache_size(thd);
  return false;
}

static Sys_var_ulong Sys_binlog_cache_size(
       "binlog_cache_size", "The size of the transactional cache for "
       "updates to transactional engines for the binary log. "
       "If you often use transactions containing many statements, "
       "you can increase this to get more performance",
       GLOBAL_VAR(binlog_cache_size),
       CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(IO_SIZE, ULONG_MAX), DEFAULT(32768), BLOCK_SIZE(IO_SIZE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_binlog_cache_size));

static Sys_var_ulong Sys_binlog_stmt_cache_size(
       "binlog_stmt_cache_size", "The size of the statement cache for "
       "updates to non-transactional engines for the binary log. "
       "If you often use statements updating a great number of rows, "
       "you can increase this to get more performance",
       GLOBAL_VAR(binlog_stmt_cache_size),
       CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(IO_SIZE, ULONG_MAX), DEFAULT(32768), BLOCK_SIZE(IO_SIZE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_binlog_stmt_cache_size));

static Sys_var_int32 Sys_binlog_max_flush_queue_time(
       "binlog_max_flush_queue_time",
       "The maximum time that the binary log group commit will keep reading"
       " transactions before it flush the transactions to the binary log (and"
       " optionally sync, depending on the value of sync_binlog).",
       GLOBAL_VAR(opt_binlog_max_flush_queue_time),
       CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 100000), DEFAULT(0), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG);

static bool check_has_super(sys_var *self, THD *thd, set_var *var)
{
  DBUG_ASSERT(self->scope() != sys_var::GLOBAL);// don't abuse check_has_super()
#ifndef NO_EMBEDDED_ACCESS_CHECKS
  if (!(thd->security_ctx->master_access & SUPER_ACL))
  {
    my_error(ER_SPECIFIC_ACCESS_DENIED_ERROR, MYF(0), "SUPER");
    return true;
  }
#endif
  return false;
}

#if defined(HAVE_GTID_NEXT_LIST) || defined(NON_DISABLED_GTID) || defined(HAVE_REPLICATION)
static bool check_top_level_stmt(sys_var *self, THD *thd, set_var *var)
{
  if (thd->in_sub_stmt)
  {
    my_error(ER_VARIABLE_NOT_SETTABLE_IN_SF_OR_TRIGGER, MYF(0), var->var->name.str);
    return true;
  }
  return false;
}

static bool check_top_level_stmt_and_super(sys_var *self, THD *thd, set_var *var)
{
  return (check_has_super(self, thd, var) ||
          check_top_level_stmt(self, thd, var));
}
#endif

#if defined(HAVE_GTID_NEXT_LIST) || defined(HAVE_REPLICATION)
static bool check_outside_transaction(sys_var *self, THD *thd, set_var *var)
{
  if (thd->in_active_multi_stmt_transaction())
  {
    my_error(ER_VARIABLE_NOT_SETTABLE_IN_TRANSACTION, MYF(0), var->var->name.str);
    return true;
  }
  return false;
}
static bool check_outside_sp(sys_var *self, THD *thd, set_var *var)
{
  if (thd->lex->sphead)
  {
    my_error(ER_VARIABLE_NOT_SETTABLE_IN_SP, MYF(0), var->var->name.str);
    return true;
  }
  return false;
}
#endif

static bool binlog_format_check(sys_var *self, THD *thd, set_var *var)
{
  if (check_has_super(self, thd, var))
    return true;

  if (var->type == OPT_GLOBAL)
    return false;

  /*
     If RBR and open temporary tables, their CREATE TABLE may not be in the
     binlog, so we can't toggle to SBR in this connection.

     If binlog_format=MIXED, there are open temporary tables, and an unsafe
     statement is executed, then subsequent statements are logged in row
     format and hence changes to temporary tables may be lost. So we forbid
     switching @@SESSION.binlog_format from MIXED to STATEMENT when there are
     open temp tables and we are logging in row format.
  */
  if (thd->temporary_tables && var->type == OPT_SESSION &&
      var->save_result.ulonglong_value == BINLOG_FORMAT_STMT &&
      ((thd->variables.binlog_format == BINLOG_FORMAT_MIXED &&
        thd->is_current_stmt_binlog_format_row()) ||
       thd->variables.binlog_format == BINLOG_FORMAT_ROW))
  {
    my_error(ER_TEMP_TABLE_PREVENTS_SWITCH_OUT_OF_RBR, MYF(0));
    return true;
  }

  /*
    if in a stored function/trigger, it's too late to change mode
  */
  if (thd->in_sub_stmt)
  {
    my_error(ER_STORED_FUNCTION_PREVENTS_SWITCH_BINLOG_FORMAT, MYF(0));
    return true;
  }
  /*
    Make the session variable 'binlog_format' read-only inside a transaction.
  */
  if (thd->in_active_multi_stmt_transaction())
  {
    my_error(ER_INSIDE_TRANSACTION_PREVENTS_SWITCH_BINLOG_FORMAT, MYF(0));
    return true;
  }

  return false;
}

static bool fix_binlog_format_after_update(sys_var *self, THD *thd,
                                           enum_var_type type)
{
  if (type == OPT_SESSION)
    thd->reset_current_stmt_binlog_format_row();
  return false;
}

static Sys_var_test_flag Sys_core_file(
       "core_file", "write a core-file on crashes", TEST_CORE_ON_SIGNAL);

static Sys_var_enum Sys_binlog_format(
       "binlog_format", "What form of binary logging the master will "
       "use: either ROW for row-based binary logging, STATEMENT "
       "for statement-based binary logging, or MIXED. MIXED is statement-"
       "based binary logging except for those statements where only row-"
       "based is correct: those which involve user-defined functions (i.e. "
       "UDFs) or the UUID() function; for those, row-based binary logging is "
       "automatically used. If NDBCLUSTER is enabled and binlog-format is "
       "MIXED, the format switches to row-based and back implicitly per each "
       "query accessing an NDBCLUSTER table",
       SESSION_VAR(binlog_format), CMD_LINE(REQUIRED_ARG, OPT_BINLOG_FORMAT),
       binlog_format_names, DEFAULT(BINLOG_FORMAT_STMT),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(binlog_format_check),
       ON_UPDATE(fix_binlog_format_after_update));

static const char *binlog_row_image_names[]= {"MINIMAL", "NOBLOB", "FULL", NullS};
static Sys_var_enum Sys_binlog_row_image(
       "binlog_row_image", 
       "Controls whether rows should be logged in 'FULL', 'NOBLOB' or "
       "'MINIMAL' formats. 'FULL', means that all columns in the before "
       "and after image are logged. 'NOBLOB', means that mysqld avoids logging "
       "blob columns whenever possible (eg, blob column was not changed or "
       "is not part of primary key). 'MINIMAL', means that a PK equivalent (PK "
       "columns or full row if there is no PK in the table) is logged in the "
       "before image, and only changed columns are logged in the after image. "
       "(Default: FULL).",
       SESSION_VAR(binlog_row_image), CMD_LINE(REQUIRED_ARG),
       binlog_row_image_names, DEFAULT(BINLOG_ROW_IMAGE_FULL),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(NULL),
       ON_UPDATE(NULL));

static bool binlog_direct_check(sys_var *self, THD *thd, set_var *var)
{
  if (check_has_super(self, thd, var))
    return true;

  if (var->type == OPT_GLOBAL)
    return false;

   /*
     Makes the session variable 'binlog_direct_non_transactional_updates'
     read-only if within a procedure, trigger or function.
   */
   if (thd->in_sub_stmt)
   {
     my_error(ER_STORED_FUNCTION_PREVENTS_SWITCH_BINLOG_DIRECT, MYF(0));
     return true;
   }
   /*
     Makes the session variable 'binlog_direct_non_transactional_updates'
     read-only inside a transaction.
   */
   if (thd->in_active_multi_stmt_transaction())
   {
     my_error(ER_INSIDE_TRANSACTION_PREVENTS_SWITCH_BINLOG_DIRECT, MYF(0));
     return true;
   }

  return false;
}

static Sys_var_mybool Sys_binlog_direct(
       "binlog_direct_non_transactional_updates",
       "Causes updates to non-transactional engines using statement format to "
       "be written directly to binary log. Before using this option make sure "
       "that there are no dependencies between transactional and "
       "non-transactional tables such as in the statement INSERT INTO t_myisam "
       "SELECT * FROM t_innodb; otherwise, slaves may diverge from the master.",
       SESSION_VAR(binlog_direct_non_trans_update),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(binlog_direct_check));

static Sys_var_mybool Sys_explicit_defaults_for_timestamp(
       "explicit_defaults_for_timestamp",
       "This option causes CREATE TABLE to create all TIMESTAMP columns "
       "as NULL with DEFAULT NULL attribute, Without this option, "
       "TIMESTAMP columns are NOT NULL and have implicit DEFAULT clauses. "
       "The old behavior is deprecated.",
       READ_ONLY SESSION_VAR(explicit_defaults_for_timestamp),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static bool repository_check(sys_var *self, THD *thd, set_var *var, SLAVE_THD_TYPE thread_mask)
{
  bool ret= FALSE;
#ifndef NO_EMBEDDED_ACCESS_CHECKS
  if (!(thd->security_ctx->master_access & SUPER_ACL))
  {
    my_error(ER_SPECIFIC_ACCESS_DENIED_ERROR, MYF(0), "SUPER");
    return TRUE;
  }
#endif
#ifdef HAVE_REPLICATION
  int running= 0;
  const char *msg= NULL;
  mysql_mutex_lock(&LOCK_active_mi);
  if (active_mi != NULL)
  {
    lock_slave_threads(active_mi);
    init_thread_mask(&running, active_mi, FALSE);
    if(!running)
    {
      switch (thread_mask)
      {
        case SLAVE_THD_IO:
        if (Rpl_info_factory::change_mi_repository(active_mi,
                                                   var->save_result.ulonglong_value,
                                                   &msg))
        {
          ret= TRUE;
          my_error(ER_CHANGE_RPL_INFO_REPOSITORY_FAILURE, MYF(0), msg);
        }
        break;
        case SLAVE_THD_SQL:
          mts_recovery_groups(active_mi->rli);
          if (!active_mi->rli->is_mts_recovery())
          {
            if (Rpl_info_factory::reset_workers(active_mi->rli) ||
                Rpl_info_factory::change_rli_repository(active_mi->rli,
                                                        var->save_result.ulonglong_value,
                                                        &msg))
            {
              ret= TRUE;
              my_error(ER_CHANGE_RPL_INFO_REPOSITORY_FAILURE, MYF(0), msg);
            }
          }
          else
            sql_print_warning("It is not possible to change the type of the "
                              "relay log's repository because there are workers' "
                              "repositories with gaps. Please, fix the gaps first "
                              "before doing such change.");
        break;
        default:
          assert(0);
        break;
      }
    }
    else
    {
      ret= TRUE;
      my_error(ER_SLAVE_MUST_STOP, MYF(0));
    }
    unlock_slave_threads(active_mi);
  }
  mysql_mutex_unlock(&LOCK_active_mi);
#endif
  return ret;
}

static bool relay_log_info_repository_check(sys_var *self, THD *thd, set_var *var)
{
  return repository_check(self, thd, var, SLAVE_THD_SQL);
}

static bool master_info_repository_check(sys_var *self, THD *thd, set_var *var)
{
  return repository_check(self, thd, var, SLAVE_THD_IO);
}

static const char *repository_names[]=
{
  "FILE", "TABLE",
#ifndef DBUG_OFF
  "DUMMY",
#endif
  0
};

ulong opt_mi_repository_id= INFO_REPOSITORY_FILE;
static Sys_var_enum Sys_mi_repository(
       "master_info_repository",
       "Defines the type of the repository for the master information."
       ,GLOBAL_VAR(opt_mi_repository_id), CMD_LINE(REQUIRED_ARG),
       repository_names, DEFAULT(INFO_REPOSITORY_FILE), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(master_info_repository_check),
       ON_UPDATE(0));

ulong opt_rli_repository_id= INFO_REPOSITORY_FILE;
static Sys_var_enum Sys_rli_repository(
       "relay_log_info_repository",
       "Defines the type of the repository for the relay log information "
       "and associated workers."
       ,GLOBAL_VAR(opt_rli_repository_id), CMD_LINE(REQUIRED_ARG),
       repository_names, DEFAULT(INFO_REPOSITORY_FILE), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(relay_log_info_repository_check),
       ON_UPDATE(0));

static Sys_var_mybool Sys_binlog_rows_query(
       "binlog_rows_query_log_events",
       "Allow writing of Rows_query_log events into binary log.",
       SESSION_VAR(binlog_rows_query_log_events),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_mybool Sys_binlog_order_commits(
       "binlog_order_commits",
       "Issue internal commit calls in the same order as transactions are"
       " written to the binary log. Default is to order commits.",
       GLOBAL_VAR(opt_binlog_order_commits),
       CMD_LINE(OPT_ARG), DEFAULT(TRUE));

static Sys_var_ulong Sys_bulk_insert_buff_size(
       "bulk_insert_buffer_size", "Size of tree cache used in bulk "
       "insert optimisation. Note that this is a limit per thread!",
       SESSION_VAR(bulk_insert_buff_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, ULONG_MAX), DEFAULT(8192*1024), BLOCK_SIZE(1));

static Sys_var_charptr Sys_character_sets_dir(
       "character_sets_dir", "Directory where character sets are",
       READ_ONLY GLOBAL_VAR(charsets_dir), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static bool check_not_null(sys_var *self, THD *thd, set_var *var)
{
  return var->value && var->value->is_null();
}
static bool check_charset(sys_var *self, THD *thd, set_var *var)
{
  if (!var->value)
    return false;

  char buff[STRING_BUFFER_USUAL_SIZE];
  if (var->value->result_type() == STRING_RESULT)
  {
    String str(buff, sizeof(buff), system_charset_info), *res;
    if (!(res= var->value->val_str(&str)))
      var->save_result.ptr= NULL;
    else
    {
      ErrConvString err(res); /* Get utf8 '\0' terminated string */
      if (!(var->save_result.ptr= get_charset_by_csname(err.ptr(),
                                                         MY_CS_PRIMARY,
                                                         MYF(0))) &&
          !(var->save_result.ptr= get_old_charset_by_name(err.ptr())))
      {
        my_error(ER_UNKNOWN_CHARACTER_SET, MYF(0), err.ptr());
        return true;
      }
    }
  }
  else // INT_RESULT
  {
    int csno= (int)var->value->val_int();
    if (!(var->save_result.ptr= get_charset(csno, MYF(0))))
    {
      my_error(ER_UNKNOWN_CHARACTER_SET, MYF(0), llstr(csno, buff));
      return true;
    }
  }
  return false;
}
static bool check_charset_not_null(sys_var *self, THD *thd, set_var *var)
{
  return check_charset(self, thd, var) || check_not_null(self, thd, var);
}
static Sys_var_struct Sys_character_set_system(
       "character_set_system", "The character set used by the server "
       "for storing identifiers",
       READ_ONLY GLOBAL_VAR(system_charset_info), NO_CMD_LINE,
       offsetof(CHARSET_INFO, csname), DEFAULT(0));

static Sys_var_struct Sys_character_set_server(
       "character_set_server", "The default character set",
       SESSION_VAR(collation_server), NO_CMD_LINE,
       offsetof(CHARSET_INFO, csname), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_charset_not_null));

static bool check_charset_db(sys_var *self, THD *thd, set_var *var)
{
  if (check_charset_not_null(self, thd, var))
    return true;
  if (!var->value) // = DEFAULT
    var->save_result.ptr= thd->db_charset;
  return false;
}
static Sys_var_struct Sys_character_set_database(
       "character_set_database",
       " The character set used by the default database",
       SESSION_VAR(collation_database), NO_CMD_LINE,
       offsetof(CHARSET_INFO, csname), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_charset_db));

static bool check_cs_client(sys_var *self, THD *thd, set_var *var)
{
  if (check_charset_not_null(self, thd, var))
    return true;

  // Currently, UCS-2 cannot be used as a client character set
  if (((CHARSET_INFO *)(var->save_result.ptr))->mbminlen > 1)
    return true;

  return false;
}
static bool fix_thd_charset(sys_var *self, THD *thd, enum_var_type type)
{
  if (type == OPT_SESSION)
    thd->update_charset();
  return false;
}
static Sys_var_struct Sys_character_set_client(
       "character_set_client", "The character set for statements "
       "that arrive from the client",
       SESSION_VAR(character_set_client), NO_CMD_LINE,
       offsetof(CHARSET_INFO, csname), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_cs_client),
       ON_UPDATE(fix_thd_charset));

static Sys_var_struct Sys_character_set_connection(
       "character_set_connection", "The character set used for "
       "literals that do not have a character set introducer and for "
       "number-to-string conversion",
       SESSION_VAR(collation_connection), NO_CMD_LINE,
       offsetof(CHARSET_INFO, csname), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_charset_not_null),
       ON_UPDATE(fix_thd_charset));

static Sys_var_struct Sys_character_set_results(
       "character_set_results", "The character set used for returning "
       "query results to the client",
       SESSION_VAR(character_set_results), NO_CMD_LINE,
       offsetof(CHARSET_INFO, csname), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_charset));

static Sys_var_struct Sys_character_set_filesystem(
       "character_set_filesystem", "The filesystem character set",
       SESSION_VAR(character_set_filesystem), NO_CMD_LINE,
       offsetof(CHARSET_INFO, csname), DEFAULT(&character_set_filesystem),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_charset_not_null),
       ON_UPDATE(fix_thd_charset));

static const char *completion_type_names[]= {"NO_CHAIN", "CHAIN", "RELEASE", 0};
static Sys_var_enum Sys_completion_type(
       "completion_type", "The transaction completion type, one of "
       "NO_CHAIN, CHAIN, RELEASE",
       SESSION_VAR(completion_type), CMD_LINE(REQUIRED_ARG),
       completion_type_names, DEFAULT(0));

static bool check_collation_not_null(sys_var *self, THD *thd, set_var *var)
{
  if (!var->value)
    return false;

  char buff[STRING_BUFFER_USUAL_SIZE];
  if (var->value->result_type() == STRING_RESULT)
  {
    String str(buff, sizeof(buff), system_charset_info), *res;
    if (!(res= var->value->val_str(&str)))
      var->save_result.ptr= NULL;
    else
    {
      ErrConvString err(res); /* Get utf8 '\0'-terminated string */
      if (!(var->save_result.ptr= get_charset_by_name(err.ptr(), MYF(0))))
      {
        my_error(ER_UNKNOWN_COLLATION, MYF(0), err.ptr());
        return true;
      }
    }
  }
  else // INT_RESULT
  {
    int csno= (int)var->value->val_int();
    if (!(var->save_result.ptr= get_charset(csno, MYF(0))))
    {
      my_error(ER_UNKNOWN_COLLATION, MYF(0), llstr(csno, buff));
      return true;
    }
  }
  return check_not_null(self, thd, var);
}
static Sys_var_struct Sys_collation_connection(
       "collation_connection", "The collation of the connection "
       "character set",
       SESSION_VAR(collation_connection), NO_CMD_LINE,
       offsetof(CHARSET_INFO, name), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_collation_not_null),
       ON_UPDATE(fix_thd_charset));

static bool check_collation_db(sys_var *self, THD *thd, set_var *var)
{
  if (check_collation_not_null(self, thd, var))
    return true;
  if (!var->value) // = DEFAULT
    var->save_result.ptr= thd->db_charset;
  return false;
}
static Sys_var_struct Sys_collation_database(
       "collation_database", "The collation of the database "
       "character set",
       SESSION_VAR(collation_database), NO_CMD_LINE,
       offsetof(CHARSET_INFO, name), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_collation_db));

static Sys_var_struct Sys_collation_server(
       "collation_server", "The server default collation",
       SESSION_VAR(collation_server), NO_CMD_LINE,
       offsetof(CHARSET_INFO, name), DEFAULT(&default_charset_info),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_collation_not_null));

static const char *concurrent_insert_names[]= {"NEVER", "AUTO", "ALWAYS", 0};
static Sys_var_enum Sys_concurrent_insert(
       "concurrent_insert", "Use concurrent insert with MyISAM. Possible "
       "values are NEVER, AUTO, ALWAYS",
       GLOBAL_VAR(myisam_concurrent_insert), CMD_LINE(OPT_ARG),
       concurrent_insert_names, DEFAULT(1));

static Sys_var_ulong Sys_connect_timeout(
       "connect_timeout",
       "The number of seconds the mysqld server is waiting for a connect "
       "packet before responding with 'Bad handshake'",
       GLOBAL_VAR(connect_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(2, LONG_TIMEOUT), DEFAULT(CONNECT_TIMEOUT), BLOCK_SIZE(1));

static Sys_var_charptr Sys_datadir(
       "datadir", "Path to the database root directory",
       READ_ONLY GLOBAL_VAR(mysql_real_data_home_ptr),
       CMD_LINE(REQUIRED_ARG, 'h'), IN_FS_CHARSET, DEFAULT(mysql_real_data_home));

#ifndef DBUG_OFF
static Sys_var_dbug Sys_dbug(
       "debug", "Debug log", sys_var::SESSION,
       CMD_LINE(OPT_ARG, '#'), DEFAULT(""), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_has_super));
#endif

export bool fix_delay_key_write(sys_var *self, THD *thd, enum_var_type type)
{
  switch (delay_key_write_options) {
  case DELAY_KEY_WRITE_NONE:
    myisam_delay_key_write=0;
    break;
  case DELAY_KEY_WRITE_ON:
    myisam_delay_key_write=1;
    break;
  case DELAY_KEY_WRITE_ALL:
    myisam_delay_key_write=1;
    ha_open_options|= HA_OPEN_DELAY_KEY_WRITE;
    break;
  }
  return false;
}
static const char *delay_key_write_names[]= { "OFF", "ON", "ALL", NullS };
static Sys_var_enum Sys_delay_key_write(
       "delay_key_write", "Type of DELAY_KEY_WRITE",
       GLOBAL_VAR(delay_key_write_options), CMD_LINE(OPT_ARG),
       delay_key_write_names, DEFAULT(DELAY_KEY_WRITE_ON),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_delay_key_write));

static Sys_var_ulong Sys_delayed_insert_limit(
       "delayed_insert_limit",
       "After inserting delayed_insert_limit rows, the INSERT DELAYED "
       "handler will check if there are any SELECT statements pending. "
       "If so, it allows these to execute before continuing. "
       "This variable is deprecated along with INSERT DELAYED.",
       GLOBAL_VAR(delayed_insert_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, ULONG_MAX), DEFAULT(DELAYED_LIMIT), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0),
       DEPRECATED(""));

static Sys_var_ulong Sys_delayed_insert_timeout(
       "delayed_insert_timeout",
       "How long a INSERT DELAYED thread should wait for INSERT statements "
       "before terminating."
       "This variable is deprecated along with INSERT DELAYED.",
       GLOBAL_VAR(delayed_insert_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, LONG_TIMEOUT), DEFAULT(DELAYED_WAIT_TIMEOUT),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(0), DEPRECATED(""));

static Sys_var_ulong Sys_delayed_queue_size(
       "delayed_queue_size",
       "What size queue (in rows) should be allocated for handling INSERT "
       "DELAYED. If the queue becomes full, any client that does INSERT "
       "DELAYED will wait until there is room in the queue again."
       "This variable is deprecated along with INSERT DELAYED.",
       GLOBAL_VAR(delayed_queue_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, ULONG_MAX), DEFAULT(DELAYED_QUEUE_SIZE), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0),
       DEPRECATED(""));

#ifdef HAVE_EVENT_SCHEDULER
static const char *event_scheduler_names[]= { "OFF", "ON", "DISABLED", NullS };
static bool event_scheduler_check(sys_var *self, THD *thd, set_var *var)
{
  /* DISABLED is only accepted on the command line */
  if (var->save_result.ulonglong_value == Events::EVENTS_DISABLED)
    return true;
  /*
    If the scheduler was disabled because there are no/bad
    system tables, produce a more meaningful error message
    than ER_OPTION_PREVENTS_STATEMENT
  */
  if (Events::check_if_system_tables_error())
    return true;
  if (Events::opt_event_scheduler == Events::EVENTS_DISABLED)
  {
    my_error(ER_OPTION_PREVENTS_STATEMENT, MYF(0),
             "--event-scheduler=DISABLED or --skip-grant-tables");
    return true;
  }
  return false;
}
static bool event_scheduler_update(sys_var *self, THD *thd, enum_var_type type)
{
  int err_no= 0;
  uint opt_event_scheduler_value= Events::opt_event_scheduler;
  mysql_mutex_unlock(&LOCK_global_system_variables);
  /*
    Events::start() is heavyweight. In particular it creates a new THD,
    which takes LOCK_global_system_variables internally.
    Thus we have to release it here.
    We need to re-take it before returning, though.

    Note that since we release LOCK_global_system_variables before calling
    start/stop, there is a possibility that the server variable
    can become out of sync with the real event scheduler state.

    This can happen with two concurrent statments if the first gets
    interrupted after start/stop but before retaking
    LOCK_global_system_variables. However, this problem should be quite
    rare and it's difficult to avoid it without opening up possibilities
    for deadlocks. See bug#51160.
  */
  bool ret= opt_event_scheduler_value == Events::EVENTS_ON
            ? Events::start(&err_no)
            : Events::stop();
  mysql_mutex_lock(&LOCK_global_system_variables);
  if (ret)
  {
    Events::opt_event_scheduler= Events::EVENTS_OFF;
    my_error(ER_EVENT_SET_VAR_ERROR, MYF(0), err_no);
  }
  return ret;
}

static Sys_var_enum Sys_event_scheduler(
       "event_scheduler", "Enable the event scheduler. Possible values are "
       "ON, OFF, and DISABLED (keep the event scheduler completely "
       "deactivated, it cannot be activated run-time)",
       GLOBAL_VAR(Events::opt_event_scheduler), CMD_LINE(OPT_ARG),
       event_scheduler_names, DEFAULT(Events::EVENTS_OFF),
       NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(event_scheduler_check), ON_UPDATE(event_scheduler_update));
#endif

static Sys_var_ulong Sys_expire_logs_days(
       "expire_logs_days",
       "If non-zero, binary logs will be purged after expire_logs_days "
       "days; possible purges happen at startup and at binary log rotation",
       GLOBAL_VAR(expire_logs_days),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 99), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_mybool Sys_flush(
       "flush", "Flush MyISAM tables to disk between SQL commands",
       GLOBAL_VAR(myisam_flush),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_ulong Sys_flush_time(
       "flush_time",
       "A dedicated thread is created to flush all tables at the "
       "given interval",
       GLOBAL_VAR(flush_time),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, LONG_TIMEOUT),
       DEFAULT(0), BLOCK_SIZE(1));

static bool check_ftb_syntax(sys_var *self, THD *thd, set_var *var)
{
  return ft_boolean_check_syntax_string((uchar*)
                      (var->save_result.string_value.str));
}
static bool query_cache_flush(sys_var *self, THD *thd, enum_var_type type)
{
#ifdef HAVE_QUERY_CACHE
  query_cache.flush();
#endif /* HAVE_QUERY_CACHE */
  return false;
}
static Sys_var_charptr Sys_ft_boolean_syntax(
       "ft_boolean_syntax", "List of operators for "
       "MATCH ... AGAINST ( ... IN BOOLEAN MODE)",
       GLOBAL_VAR(ft_boolean_syntax),
       CMD_LINE(REQUIRED_ARG), IN_SYSTEM_CHARSET,
       DEFAULT(DEFAULT_FTB_SYNTAX), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(check_ftb_syntax), ON_UPDATE(query_cache_flush));

static Sys_var_ulong Sys_ft_max_word_len(
       "ft_max_word_len",
       "The maximum length of the word to be included in a FULLTEXT index. "
       "Note: FULLTEXT indexes must be rebuilt after changing this variable",
       READ_ONLY GLOBAL_VAR(ft_max_word_len), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(10, HA_FT_MAXCHARLEN), DEFAULT(HA_FT_MAXCHARLEN),
       BLOCK_SIZE(1));

static Sys_var_ulong Sys_ft_min_word_len(
       "ft_min_word_len",
       "The minimum length of the word to be included in a FULLTEXT index. "
       "Note: FULLTEXT indexes must be rebuilt after changing this variable",
       READ_ONLY GLOBAL_VAR(ft_min_word_len), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, HA_FT_MAXCHARLEN), DEFAULT(4), BLOCK_SIZE(1));

static Sys_var_ulong Sys_ft_query_expansion_limit(
       "ft_query_expansion_limit",
       "Number of best matches to use for query expansion",
       READ_ONLY GLOBAL_VAR(ft_query_expansion_limit),
       CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 1000), DEFAULT(20), BLOCK_SIZE(1));

static Sys_var_charptr Sys_ft_stopword_file(
       "ft_stopword_file",
       "Use stopwords from this file instead of built-in list",
       READ_ONLY GLOBAL_VAR(ft_stopword_file), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_mybool Sys_ignore_builtin_innodb(
       "ignore_builtin_innodb",
       "IGNORED. This option will be removed in future releases. "
       "Disable initialization of builtin InnoDB plugin",
       READ_ONLY GLOBAL_VAR(opt_ignore_builtin_innodb),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static bool check_init_string(sys_var *self, THD *thd, set_var *var)
{
  if (var->save_result.string_value.str == 0)
  {
    var->save_result.string_value.str= const_cast<char*>("");
    var->save_result.string_value.length= 0;
  }
  return false;
}
static PolyLock_rwlock PLock_sys_init_connect(&LOCK_sys_init_connect);
static Sys_var_lexstring Sys_init_connect(
       "init_connect", "Command(s) that are executed for each "
       "new connection", GLOBAL_VAR(opt_init_connect),
       CMD_LINE(REQUIRED_ARG), IN_SYSTEM_CHARSET,
       DEFAULT(""), &PLock_sys_init_connect, NOT_IN_BINLOG,
       ON_CHECK(check_init_string));

static Sys_var_charptr Sys_init_file(
       "init_file", "Read SQL commands from this file at startup",
       READ_ONLY GLOBAL_VAR(opt_init_file),
#ifdef DISABLE_GRANT_OPTIONS
       NO_CMD_LINE,
#else
       CMD_LINE(REQUIRED_ARG),
#endif
       IN_FS_CHARSET, DEFAULT(0));

static PolyLock_rwlock PLock_sys_init_slave(&LOCK_sys_init_slave);
static Sys_var_lexstring Sys_init_slave(
       "init_slave", "Command(s) that are executed by a slave server "
       "each time the SQL thread starts", GLOBAL_VAR(opt_init_slave),
       CMD_LINE(REQUIRED_ARG), IN_SYSTEM_CHARSET,
       DEFAULT(""), &PLock_sys_init_slave,
       NOT_IN_BINLOG, ON_CHECK(check_init_string));

static Sys_var_ulong Sys_interactive_timeout(
       "interactive_timeout",
       "The number of seconds the server waits for activity on an interactive "
       "connection before closing it",
       SESSION_VAR(net_interactive_timeout),
       CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, LONG_TIMEOUT), DEFAULT(NET_WAIT_TIMEOUT), BLOCK_SIZE(1));

static Sys_var_ulong Sys_join_buffer_size(
       "join_buffer_size",
       "The size of the buffer that is used for full joins",
       SESSION_VAR(join_buff_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(128, ULONG_MAX), DEFAULT(256 * 1024), BLOCK_SIZE(128));

static Sys_var_keycache Sys_key_buffer_size(
       "key_buffer_size", "The size of the buffer used for "
       "index blocks for MyISAM tables. Increase this to get better index "
       "handling (for all reads and multiple writes) to as much as you can "
       "afford",
       KEYCACHE_VAR(param_buff_size),
       CMD_LINE(REQUIRED_ARG, OPT_KEY_BUFFER_SIZE),
       VALID_RANGE(0, SIZE_T_MAX), DEFAULT(KEY_CACHE_SIZE),
       BLOCK_SIZE(IO_SIZE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_buffer_size));

static Sys_var_keycache Sys_key_cache_block_size(
       "key_cache_block_size", "The default size of key cache blocks",
       KEYCACHE_VAR(param_block_size),
       CMD_LINE(REQUIRED_ARG, OPT_KEY_CACHE_BLOCK_SIZE),
       VALID_RANGE(512, 1024*16), DEFAULT(KEY_CACHE_BLOCK_SIZE),
       BLOCK_SIZE(512), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_keycache_param));

static Sys_var_keycache Sys_key_cache_division_limit(
       "key_cache_division_limit",
       "The minimum percentage of warm blocks in key cache",
       KEYCACHE_VAR(param_division_limit),
       CMD_LINE(REQUIRED_ARG, OPT_KEY_CACHE_DIVISION_LIMIT),
       VALID_RANGE(1, 100), DEFAULT(100),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_keycache_param));

static Sys_var_keycache Sys_key_cache_age_threshold(
       "key_cache_age_threshold", "This characterizes the number of "
       "hits a hot block has to be untouched until it is considered aged "
       "enough to be downgraded to a warm block. This specifies the "
       "percentage ratio of that number of hits to the total number of "
       "blocks in key cache",
       KEYCACHE_VAR(param_age_threshold),
       CMD_LINE(REQUIRED_ARG, OPT_KEY_CACHE_AGE_THRESHOLD),
       VALID_RANGE(100, ULONG_MAX), DEFAULT(300),
       BLOCK_SIZE(100), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_keycache_param));

static Sys_var_mybool Sys_large_files_support(
       "large_files_support",
       "Whether mysqld was compiled with options for large file support",
       READ_ONLY GLOBAL_VAR(opt_large_files),
       NO_CMD_LINE, DEFAULT(sizeof(my_off_t) > 4));

static Sys_var_uint Sys_large_page_size(
       "large_page_size",
       "If large page support is enabled, this shows the size of memory pages",
       READ_ONLY GLOBAL_VAR(opt_large_page_size), NO_CMD_LINE,
       VALID_RANGE(0, UINT_MAX), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_mybool Sys_large_pages(
       "large_pages", "Enable support for large pages",
       READ_ONLY GLOBAL_VAR(opt_large_pages),
       IF_WIN(NO_CMD_LINE, CMD_LINE(OPT_ARG)), DEFAULT(FALSE));

static Sys_var_charptr Sys_language(
       "lc_messages_dir", "Directory where error messages are",
       READ_ONLY GLOBAL_VAR(lc_messages_dir_ptr), 
       CMD_LINE(REQUIRED_ARG, OPT_LC_MESSAGES_DIRECTORY),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_mybool Sys_local_infile(
       "local_infile", "Enable LOAD DATA LOCAL INFILE",
       GLOBAL_VAR(opt_local_infile), CMD_LINE(OPT_ARG), DEFAULT(TRUE));

static Sys_var_ulong Sys_lock_wait_timeout(
       "lock_wait_timeout",
       "Timeout in seconds to wait for a lock before returning an error.",
       SESSION_VAR(lock_wait_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, LONG_TIMEOUT), DEFAULT(LONG_TIMEOUT), BLOCK_SIZE(1));

#ifdef HAVE_MLOCKALL
static Sys_var_mybool Sys_locked_in_memory(
       "locked_in_memory",
       "Whether mysqld was locked in memory with --memlock",
       READ_ONLY GLOBAL_VAR(locked_in_memory), NO_CMD_LINE, DEFAULT(FALSE));
#endif

/* this says NO_CMD_LINE, as command-line option takes a string, not a bool */
static Sys_var_mybool Sys_log_bin(
       "log_bin", "Whether the binary log is enabled",
       READ_ONLY GLOBAL_VAR(opt_bin_log), NO_CMD_LINE, DEFAULT(FALSE));

static Sys_var_ulong Sys_rpl_stop_slave_timeout(
       "rpl_stop_slave_timeout",
       "Timeout in seconds to wait for slave to stop before returning a "
       "warning.",
       GLOBAL_VAR(rpl_stop_slave_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(2, LONG_TIMEOUT), DEFAULT(LONG_TIMEOUT), BLOCK_SIZE(1));

static Sys_var_mybool Sys_trust_function_creators(
       "log_bin_trust_function_creators",
       "If set to FALSE (the default), then when --log-bin is used, creation "
       "of a stored function (or trigger) is allowed only to users having the "
       "SUPER privilege and only if this stored function (trigger) may not "
       "break binary logging. Note that if ALL connections to this server "
       "ALWAYS use row-based binary logging, the security issues do not "
       "exist and the binary logging cannot break, so you can safely set "
       "this to TRUE",
       GLOBAL_VAR(trust_function_creators),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_mybool Sys_use_v1_row_events(
       "log_bin_use_v1_row_events",
       "If equal to 1 then version 1 row events are written to a row based "
       "binary log.  If equal to 0, then the latest version of events are "
       "written.  "
       "This option is useful during some upgrades.",
       GLOBAL_VAR(log_bin_use_v1_row_events),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_charptr Sys_log_error(
       "log_error", "Error log file",
       READ_ONLY GLOBAL_VAR(log_error_file_ptr),
       CMD_LINE(OPT_ARG, OPT_LOG_ERROR),
       IN_FS_CHARSET, DEFAULT(disabled_my_option));

static Sys_var_mybool Sys_log_queries_not_using_indexes(
       "log_queries_not_using_indexes",
       "Log queries that are executed without benefit of any index to the "
       "slow log if it is open",
       GLOBAL_VAR(opt_log_queries_not_using_indexes),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_mybool Sys_log_slow_admin_statements(
       "log_slow_admin_statements",
       "Log slow OPTIMIZE, ANALYZE, ALTER and other administrative statements to "
       "the slow log if it is open.",
       GLOBAL_VAR(opt_log_slow_admin_statements),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_mybool Sys_log_slow_slave_statements(
       "log_slow_slave_statements",
       "Log slow statements executed by slave thread to the slow log if it is open.",
       GLOBAL_VAR(opt_log_slow_slave_statements),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static bool update_log_throttle_queries_not_using_indexes(sys_var *self,
                                                          THD *thd,
                                                          enum_var_type type)
{
  // Check if we should print a summary of any suppressed lines to the slow log
  // now since opt_log_throttle_queries_not_using_indexes was changed.
  log_throttle_qni.flush(thd);
  return false;
}

static Sys_var_ulong Sys_log_throttle_queries_not_using_indexes(
       "log_throttle_queries_not_using_indexes",
       "Log at most this many 'not using index' warnings per minute to the "
       "slow log. Any further warnings will be condensed into a single "
       "summary line. A value of 0 disables throttling. "
       "Option has no effect unless --log_queries_not_using_indexes is set.",
       GLOBAL_VAR(opt_log_throttle_queries_not_using_indexes),
       CMD_LINE(OPT_ARG),
       VALID_RANGE(0, ULONG_MAX), DEFAULT(0), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(0),
       ON_UPDATE(update_log_throttle_queries_not_using_indexes));

static Sys_var_ulong Sys_log_warnings(
       "log_warnings",
       "Log some not critical warnings to the log file",
       GLOBAL_VAR(log_warnings),
       CMD_LINE(OPT_ARG, 'W'),
       VALID_RANGE(0, ULONG_MAX), DEFAULT(1), BLOCK_SIZE(1));

static bool update_cached_long_query_time(sys_var *self, THD *thd,
                                          enum_var_type type)
{
  if (type == OPT_SESSION)
    thd->variables.long_query_time=
      double2ulonglong(thd->variables.long_query_time_double * 1e6);
  else
    global_system_variables.long_query_time=
      double2ulonglong(global_system_variables.long_query_time_double * 1e6);
  return false;
}

static Sys_var_double Sys_long_query_time(
       "long_query_time",
       "Log all queries that have taken more than long_query_time seconds "
       "to execute to file. The argument will be treated as a decimal value "
       "with microsecond precision",
       SESSION_VAR(long_query_time_double),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, LONG_TIMEOUT), DEFAULT(10),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_cached_long_query_time));

static bool fix_low_prio_updates(sys_var *self, THD *thd, enum_var_type type)
{
  if (type == OPT_SESSION)
    thd->update_lock_default= (thd->variables.low_priority_updates ?
                               TL_WRITE_LOW_PRIORITY : TL_WRITE);
  else
    thr_upgraded_concurrent_insert_lock=
      (global_system_variables.low_priority_updates ?
       TL_WRITE_LOW_PRIORITY : TL_WRITE);
  return false;
}
static Sys_var_mybool Sys_low_priority_updates(
       "low_priority_updates",
       "INSERT/DELETE/UPDATE has lower priority than selects",
       SESSION_VAR(low_priority_updates),
       CMD_LINE(OPT_ARG),
       DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_low_prio_updates));

static Sys_var_mybool Sys_lower_case_file_system(
       "lower_case_file_system",
       "Case sensitivity of file names on the file system where the "
       "data directory is located",
       READ_ONLY GLOBAL_VAR(lower_case_file_system), NO_CMD_LINE,
       DEFAULT(FALSE));

static Sys_var_uint Sys_lower_case_table_names(
       "lower_case_table_names",
       "If set to 1 table names are stored in lowercase on disk and table "
       "names will be case-insensitive.  Should be set to 2 if you are using "
       "a case insensitive file system",
       READ_ONLY GLOBAL_VAR(lower_case_table_names),
       CMD_LINE(OPT_ARG, OPT_LOWER_CASE_TABLE_NAMES),
       VALID_RANGE(0, 2),
#ifdef FN_NO_CASE_SENSE
    DEFAULT(1),
#else
    DEFAULT(0),
#endif
       BLOCK_SIZE(1));

static bool session_readonly(sys_var *self, THD *thd, set_var *var)
{
  if (var->type == OPT_GLOBAL)
    return false;
  my_error(ER_VARIABLE_IS_READONLY, MYF(0), "SESSION",
           self->name.str, "GLOBAL");
  return true;
}

static bool
check_max_allowed_packet(sys_var *self, THD *thd,  set_var *var)
{
  longlong val;
  if (session_readonly(self, thd, var))
    return true;

  val= var->save_result.ulonglong_value;
  if (val < (longlong) global_system_variables.net_buffer_length)
  {
    push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,
                        WARN_OPTION_BELOW_LIMIT, ER(WARN_OPTION_BELOW_LIMIT),
                        "max_allowed_packet", "net_buffer_length");
  }
  return false;
}


static Sys_var_ulong Sys_max_allowed_packet(
       "max_allowed_packet",
       "Max packet length to send to or receive from the server",
       SESSION_VAR(max_allowed_packet), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, 1024 * 1024 * 1024), DEFAULT(4096 * 1024),
       BLOCK_SIZE(1024), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_max_allowed_packet));

static Sys_var_ulong Sys_slave_max_allowed_packet(
       "slave_max_allowed_packet",
       "The maximum packet length to sent successfully from the master to slave.",
       GLOBAL_VAR(slave_max_allowed_packet), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, MAX_MAX_ALLOWED_PACKET),
       DEFAULT(MAX_MAX_ALLOWED_PACKET),
       BLOCK_SIZE(1024));

static Sys_var_ulonglong Sys_max_binlog_cache_size(
       "max_binlog_cache_size",
       "Sets the total size of the transactional cache",
       GLOBAL_VAR(max_binlog_cache_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(IO_SIZE, ULONGLONG_MAX),
       DEFAULT((ULONGLONG_MAX/IO_SIZE)*IO_SIZE),
       BLOCK_SIZE(IO_SIZE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_binlog_cache_size));

static Sys_var_ulonglong Sys_max_binlog_stmt_cache_size(
       "max_binlog_stmt_cache_size",
       "Sets the total size of the statement cache",
       GLOBAL_VAR(max_binlog_stmt_cache_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(IO_SIZE, ULONGLONG_MAX),
       DEFAULT((ULONGLONG_MAX/IO_SIZE)*IO_SIZE),
       BLOCK_SIZE(IO_SIZE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_binlog_stmt_cache_size));

static bool fix_max_binlog_size(sys_var *self, THD *thd, enum_var_type type)
{
  mysql_bin_log.set_max_size(max_binlog_size);
#ifdef HAVE_REPLICATION
  if (active_mi != NULL && !max_relay_log_size)
    active_mi->rli->relay_log.set_max_size(max_binlog_size);
#endif
  return false;
}
static Sys_var_ulong Sys_max_binlog_size(
       "max_binlog_size",
       "Binary log will be rotated automatically when the size exceeds this "
       "value. Will also apply to relay logs if max_relay_log_size is 0",
       GLOBAL_VAR(max_binlog_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(IO_SIZE, 1024*1024L*1024L), DEFAULT(1024*1024L*1024L),
       BLOCK_SIZE(IO_SIZE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_max_binlog_size));

static bool fix_max_connections(sys_var *self, THD *thd, enum_var_type type)
{
#ifndef EMBEDDED_LIBRARY
  resize_thr_alarm(max_connections +
                   global_system_variables.max_insert_delayed_threads + 10);
#endif
  return false;
}

static Sys_var_ulong Sys_max_connections(
       "max_connections", "The number of simultaneous clients allowed",
       GLOBAL_VAR(max_connections), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, 100000),
       DEFAULT(MAX_CONNECTIONS_DEFAULT),
       BLOCK_SIZE(1),
       NO_MUTEX_GUARD,
       NOT_IN_BINLOG,
       ON_CHECK(0),
       ON_UPDATE(fix_max_connections),
       NULL,
       /* max_connections is used as a sizing hint by the performance schema. */
       sys_var::PARSE_EARLY);

static Sys_var_ulong Sys_max_connect_errors(
       "max_connect_errors",
       "If there is more than this number of interrupted connections from "
       "a host this host will be blocked from further connections",
       GLOBAL_VAR(max_connect_errors), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, ULONG_MAX), DEFAULT(100),
       BLOCK_SIZE(1));

static bool check_max_delayed_threads(sys_var *self, THD *thd, set_var *var)
{
  return var->type != OPT_GLOBAL &&
         var->save_result.ulonglong_value != 0 &&
         var->save_result.ulonglong_value !=
                           global_system_variables.max_insert_delayed_threads;
}

// Alias for max_delayed_threads
static Sys_var_ulong Sys_max_insert_delayed_threads(
       "max_insert_delayed_threads",
       "Don't start more than this number of threads to handle INSERT "
       "DELAYED statements. If set to zero INSERT DELAYED will be not used."
       "This variable is deprecated along with INSERT DELAYED.",
       SESSION_VAR(max_insert_delayed_threads),
       NO_CMD_LINE, VALID_RANGE(0, 16384), DEFAULT(20),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_max_delayed_threads), ON_UPDATE(fix_max_connections),
       DEPRECATED(""));

static Sys_var_ulong Sys_max_delayed_threads(
       "max_delayed_threads",
       "Don't start more than this number of threads to handle INSERT "
       "DELAYED statements. If set to zero INSERT DELAYED will be not used."
       "This variable is deprecated along with INSERT DELAYED.",
       SESSION_VAR(max_insert_delayed_threads),
       CMD_LINE(REQUIRED_ARG), VALID_RANGE(0, 16384), DEFAULT(20),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_max_delayed_threads), ON_UPDATE(fix_max_connections),
       DEPRECATED(""));

static Sys_var_ulong Sys_max_error_count(
       "max_error_count",
       "Max number of errors/warnings to store for a statement",
       SESSION_VAR(max_error_count), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 65535), DEFAULT(DEFAULT_ERROR_COUNT), BLOCK_SIZE(1));

static Sys_var_ulonglong Sys_max_heap_table_size(
       "max_heap_table_size",
       "Don't allow creation of heap tables bigger than this",
       SESSION_VAR(max_heap_table_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(16384, (ulonglong)~(intptr)0), DEFAULT(16*1024*1024),
       BLOCK_SIZE(1024));

static Sys_var_ulong Sys_metadata_locks_cache_size(
       "metadata_locks_cache_size", "Size of unused metadata locks cache",
       READ_ONLY GLOBAL_VAR(mdl_locks_cache_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, 1024*1024), DEFAULT(MDL_LOCKS_CACHE_SIZE_DEFAULT),
       BLOCK_SIZE(1));

static Sys_var_ulong Sys_metadata_locks_hash_instances(
       "metadata_locks_hash_instances", "Number of metadata locks hash instances",
       READ_ONLY GLOBAL_VAR(mdl_locks_hash_partitions), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, 1024), DEFAULT(MDL_LOCKS_HASH_PARTITIONS_DEFAULT),
       BLOCK_SIZE(1));

static Sys_var_ulong Sys_pseudo_thread_id(
       "pseudo_thread_id",
       "This variable is for internal server use",
       SESSION_ONLY(pseudo_thread_id),
       NO_CMD_LINE, VALID_RANGE(0, ULONG_MAX), DEFAULT(0),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, IN_BINLOG,
       ON_CHECK(check_has_super));

static bool fix_max_join_size(sys_var *self, THD *thd, enum_var_type type)
{
  SV *sv= type == OPT_GLOBAL ? &global_system_variables : &thd->variables;
  if (sv->max_join_size == HA_POS_ERROR)
    sv->option_bits|= OPTION_BIG_SELECTS;
  else
    sv->option_bits&= ~OPTION_BIG_SELECTS;
  return false;
}
static Sys_var_harows Sys_max_join_size(
       "max_join_size",
       "Joins that are probably going to read more than max_join_size "
       "records return an error",
       SESSION_VAR(max_join_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, HA_POS_ERROR), DEFAULT(HA_POS_ERROR), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_max_join_size));

static Sys_var_ulong Sys_max_seeks_for_key(
       "max_seeks_for_key",
       "Limit assumed max number of seeks when looking up rows based on a key",
       SESSION_VAR(max_seeks_for_key), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, ULONG_MAX), DEFAULT(ULONG_MAX), BLOCK_SIZE(1));

static Sys_var_ulong Sys_max_length_for_sort_data(
       "max_length_for_sort_data",
       "Max number of bytes in sorted records",
       SESSION_VAR(max_length_for_sort_data), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(4, 8192*1024L), DEFAULT(1024), BLOCK_SIZE(1));

static PolyLock_mutex PLock_prepared_stmt_count(&LOCK_prepared_stmt_count);
static Sys_var_ulong Sys_max_prepared_stmt_count(
       "max_prepared_stmt_count",
       "Maximum number of prepared statements in the server",
       GLOBAL_VAR(max_prepared_stmt_count), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 1024*1024), DEFAULT(16382), BLOCK_SIZE(1),
       &PLock_prepared_stmt_count);

static bool fix_max_relay_log_size(sys_var *self, THD *thd, enum_var_type type)
{
#ifdef HAVE_REPLICATION
  if (active_mi != NULL)
    active_mi->rli->relay_log.set_max_size(max_relay_log_size ?
                                           max_relay_log_size: max_binlog_size);
#endif
  return false;
}
static Sys_var_ulong Sys_max_relay_log_size(
       "max_relay_log_size",
       "If non-zero: relay log will be rotated automatically when the "
       "size exceeds this value; if zero: when the size "
       "exceeds max_binlog_size",
       GLOBAL_VAR(max_relay_log_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 1024L*1024*1024), DEFAULT(0), BLOCK_SIZE(IO_SIZE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_max_relay_log_size));

static Sys_var_ulong Sys_max_sort_length(
       "max_sort_length",
       "The number of bytes to use when sorting BLOB or TEXT values (only "
       "the first max_sort_length bytes of each value are used; the rest "
       "are ignored)",
       SESSION_VAR(max_sort_length), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(4, 8192*1024L), DEFAULT(1024), BLOCK_SIZE(1));

static Sys_var_ulong Sys_max_sp_recursion_depth(
       "max_sp_recursion_depth",
       "Maximum stored procedure recursion depth",
       SESSION_VAR(max_sp_recursion_depth), CMD_LINE(OPT_ARG),
       VALID_RANGE(0, 255), DEFAULT(0), BLOCK_SIZE(1));

// non-standard session_value_ptr() here
static Sys_var_max_user_conn Sys_max_user_connections(
       "max_user_connections",
       "The maximum number of active connections for a single user "
       "(0 = no limit)",
       SESSION_VAR(max_user_connections), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(0), BLOCK_SIZE(1), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(session_readonly));

static Sys_var_ulong Sys_max_tmp_tables(
       "max_tmp_tables",
       "Maximum number of temporary tables a client can keep open at a time",
       SESSION_VAR(max_tmp_tables), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, ULONG_MAX), DEFAULT(32), BLOCK_SIZE(1), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0), DEPRECATED(""));

static Sys_var_ulong Sys_max_write_lock_count(
       "max_write_lock_count",
       "After this many write locks, allow some read locks to run in between",
       GLOBAL_VAR(max_write_lock_count), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, ULONG_MAX), DEFAULT(ULONG_MAX), BLOCK_SIZE(1));

static Sys_var_ulong Sys_min_examined_row_limit(
       "min_examined_row_limit",
       "Don't write queries to slow log that examine fewer rows "
       "than that",
       SESSION_VAR(min_examined_row_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, ULONG_MAX), DEFAULT(0), BLOCK_SIZE(1));

#ifdef _WIN32
static Sys_var_mybool Sys_named_pipe(
       "named_pipe", "Enable the named pipe (NT)",
       READ_ONLY GLOBAL_VAR(opt_enable_named_pipe), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));
#endif


static bool 
check_net_buffer_length(sys_var *self, THD *thd,  set_var *var)
{
  longlong val;
  if (session_readonly(self, thd, var))
    return true;

  val= var->save_result.ulonglong_value;
  if (val > (longlong) global_system_variables.max_allowed_packet)
  {
    push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,
                        WARN_OPTION_BELOW_LIMIT, ER(WARN_OPTION_BELOW_LIMIT),
                        "max_allowed_packet", "net_buffer_length");
  }
  return false;
}
static Sys_var_ulong Sys_net_buffer_length(
       "net_buffer_length",
       "Buffer length for TCP/IP and socket communication",
       SESSION_VAR(net_buffer_length), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, 1024*1024), DEFAULT(16384), BLOCK_SIZE(1024),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_net_buffer_length));

static bool fix_net_read_timeout(sys_var *self, THD *thd, enum_var_type type)
{
  if (type != OPT_GLOBAL)
    my_net_set_read_timeout(&thd->net, thd->variables.net_read_timeout);
  return false;
}
static Sys_var_ulong Sys_net_read_timeout(
       "net_read_timeout",
       "Number of seconds to wait for more data from a connection before "
       "aborting the read",
       SESSION_VAR(net_read_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, LONG_TIMEOUT), DEFAULT(NET_READ_TIMEOUT), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_net_read_timeout));

static bool fix_net_write_timeout(sys_var *self, THD *thd, enum_var_type type)
{
  if (type != OPT_GLOBAL)
    my_net_set_write_timeout(&thd->net, thd->variables.net_write_timeout);
  return false;
}
static Sys_var_ulong Sys_net_write_timeout(
       "net_write_timeout",
       "Number of seconds to wait for a block to be written to a connection "
       "before aborting the write",
       SESSION_VAR(net_write_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, LONG_TIMEOUT), DEFAULT(NET_WRITE_TIMEOUT), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_net_write_timeout));

static bool fix_net_retry_count(sys_var *self, THD *thd, enum_var_type type)
{
  if (type != OPT_GLOBAL)
    thd->net.retry_count=thd->variables.net_retry_count;
  return false;
}
static Sys_var_ulong Sys_net_retry_count(
       "net_retry_count",
       "If a read on a communication port is interrupted, retry this "
       "many times before giving up",
       SESSION_VAR(net_retry_count), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, ULONG_MAX), DEFAULT(MYSQLD_NET_RETRY_COUNT),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_net_retry_count));

static Sys_var_mybool Sys_new_mode(
       "new", "Use very new possible \"unsafe\" functions",
       SESSION_VAR(new_mode), CMD_LINE(OPT_ARG, 'n'), DEFAULT(FALSE));

static Sys_var_mybool Sys_old_mode(
       "old", "Use compatible behavior",
       READ_ONLY GLOBAL_VAR(old_mode), CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_mybool Sys_old_alter_table(
       "old_alter_table", "Use old, non-optimized alter table",
       SESSION_VAR(old_alter_table), CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_uint Sys_old_passwords(
       "old_passwords",
       "Determine which hash algorithm to use when generating passwords using "
       "the PASSWORD() function",
       SESSION_VAR(old_passwords), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 2), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_ulong Sys_open_files_limit(
       "open_files_limit",
       "If this is not 0, then mysqld will use this value to reserve file "
       "descriptors to use with setrlimit(). If this value is 0 then mysqld "
       "will reserve max_connections*5 or max_connections + table_cache*2 "
       "(whichever is larger) number of file descriptors",
       READ_ONLY GLOBAL_VAR(open_files_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, OS_FILE_LIMIT), DEFAULT(0), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(NULL), ON_UPDATE(NULL),
       NULL,
       /* open_files_limit is used as a sizing hint by the performance schema. */
       sys_var::PARSE_EARLY);

static Sys_var_ulong Sys_optimizer_prune_level(
       "optimizer_prune_level",
       "Controls the heuristic(s) applied during query optimization to prune "
       "less-promising partial plans from the optimizer search space. "
       "Meaning: 0 - do not apply any heuristic, thus perform exhaustive "
       "search; 1 - prune plans based on number of retrieved rows",
       SESSION_VAR(optimizer_prune_level), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 1), DEFAULT(1), BLOCK_SIZE(1));

static Sys_var_ulong Sys_optimizer_search_depth(
       "optimizer_search_depth",
       "Maximum depth of search performed by the query optimizer. Values "
       "larger than the number of relations in a query result in better "
       "query plans, but take longer to compile a query. Values smaller "
       "than the number of tables in a relation result in faster "
       "optimization, but may produce very bad query plans. If set to 0, "
       "the system will automatically pick a reasonable value",
       SESSION_VAR(optimizer_search_depth), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, MAX_TABLES+1), DEFAULT(MAX_TABLES+1), BLOCK_SIZE(1));

static const char *optimizer_switch_names[]=
{
  "index_merge", "index_merge_union", "index_merge_sort_union",
  "index_merge_intersection", "engine_condition_pushdown",
  "index_condition_pushdown" , "mrr", "mrr_cost_based",
  "block_nested_loop", "batched_key_access",
#ifdef OPTIMIZER_SWITCH_ALL
  "materialization", "semijoin", "loosescan", "firstmatch",
  "subquery_materialization_cost_based",
#endif
  "use_index_extensions", "default", NullS
};
static bool fix_optimizer_switch(sys_var *self, THD *thd,
                                 enum_var_type type)
{
  SV *sv= (type == OPT_GLOBAL) ? &global_system_variables : &thd->variables;
  sv->engine_condition_pushdown= 
    test(sv->optimizer_switch & OPTIMIZER_SWITCH_ENGINE_CONDITION_PUSHDOWN);

  return false;
}
static Sys_var_flagset Sys_optimizer_switch(
       "optimizer_switch",
       "optimizer_switch=option=val[,option=val...], where option is one of "
       "{index_merge, index_merge_union, index_merge_sort_union, "
       "index_merge_intersection, engine_condition_pushdown, "
       "index_condition_pushdown, mrr, mrr_cost_based"
#ifdef OPTIMIZER_SWITCH_ALL
       ", materialization, semijoin, loosescan, firstmatch,"
       " subquery_materialization_cost_based"
#endif
       ", block_nested_loop, batched_key_access, use_index_extensions"
       "} and val is one of {on, off, default}",
       SESSION_VAR(optimizer_switch), CMD_LINE(REQUIRED_ARG),
       optimizer_switch_names, DEFAULT(OPTIMIZER_SWITCH_DEFAULT),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(NULL),
       ON_UPDATE(fix_optimizer_switch));

static Sys_var_mybool Sys_var_end_markers_in_json(
       "end_markers_in_json",
       "In JSON output (\"EXPLAIN FORMAT=JSON\" and optimizer trace), "
       "if variable is set to 1, repeats the structure's key (if it has one) "
       "near the closing bracket",
       SESSION_VAR(end_markers_in_json), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

#ifdef OPTIMIZER_TRACE

static Sys_var_flagset Sys_optimizer_trace(
       "optimizer_trace",
       "Controls tracing of the Optimizer:"
       " optimizer_trace=option=val[,option=val...], where option is one of"
       " {enabled, one_line}"
       " and val is one of {on, default}",
       SESSION_VAR(optimizer_trace), CMD_LINE(REQUIRED_ARG),
       Opt_trace_context::flag_names,
       DEFAULT(Opt_trace_context::FLAG_DEFAULT));
// @see set_var::is_var_optimizer_trace()
export sys_var *Sys_optimizer_trace_ptr= &Sys_optimizer_trace;

static Sys_var_flagset Sys_optimizer_trace_features(
       "optimizer_trace_features",
       "Enables/disables tracing of selected features of the Optimizer:"
       " optimizer_trace_features=option=val[,option=val...], where option is one of"
       " {greedy_search, range_optimizer, dynamic_range, repeated_subselect}"
       " and val is one of {on, off, default}",
       SESSION_VAR(optimizer_trace_features), CMD_LINE(REQUIRED_ARG),
       Opt_trace_context::feature_names,
       DEFAULT(Opt_trace_context::default_features));

static bool optimizer_trace_update(sys_var *self, THD *thd,
                                   enum_var_type type)
{
  thd->opt_trace.reset();
  return false;
}

static Sys_var_long Sys_optimizer_trace_offset(
       "optimizer_trace_offset",
       "Offset of first optimizer trace to show; see manual",
       SESSION_VAR(optimizer_trace_offset), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(LONG_MIN, LONG_MAX), DEFAULT(-1), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(NULL),
       ON_UPDATE(optimizer_trace_update));

static Sys_var_long Sys_optimizer_trace_limit(
       "optimizer_trace_limit",
       "Maximum number of shown optimizer traces",
       SESSION_VAR(optimizer_trace_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, LONG_MAX), DEFAULT(1), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(NULL),
       ON_UPDATE(optimizer_trace_update));

static Sys_var_ulong Sys_optimizer_trace_max_mem_size(
       "optimizer_trace_max_mem_size",
       "Maximum allowed cumulated size of stored optimizer traces",
       SESSION_VAR(optimizer_trace_max_mem_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, ULONG_MAX), DEFAULT(1024*16), BLOCK_SIZE(1));

#endif

static Sys_var_charptr Sys_pid_file(
       "pid_file", "Pid file used by safe_mysqld",
       READ_ONLY GLOBAL_VAR(pidfile_name_ptr), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_plugin_dir(
       "plugin_dir", "Directory for plugins",
       READ_ONLY GLOBAL_VAR(opt_plugin_dir_ptr), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_uint Sys_port(
       "port",
       "Port number to use for connection or 0 to default to, "
       "my.cnf, $MYSQL_TCP_PORT, "
#if MYSQL_PORT_DEFAULT == 0
       "/etc/services, "
#endif
       "built-in default (" STRINGIFY_ARG(MYSQL_PORT) "), whatever comes first",
       READ_ONLY GLOBAL_VAR(mysqld_port), CMD_LINE(REQUIRED_ARG, 'P'),
       VALID_RANGE(0, UINT_MAX32), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_ulong Sys_preload_buff_size(
       "preload_buffer_size",
       "The size of the buffer that is allocated when preloading indexes",
       SESSION_VAR(preload_buff_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, 1024*1024*1024), DEFAULT(32768), BLOCK_SIZE(1));

static Sys_var_uint Sys_protocol_version(
       "protocol_version",
       "The version of the client/server protocol used by the MySQL server",
       READ_ONLY GLOBAL_VAR(protocol_version), NO_CMD_LINE,
       VALID_RANGE(0, ~0), DEFAULT(PROTOCOL_VERSION), BLOCK_SIZE(1));

static Sys_var_proxy_user Sys_proxy_user(
       "proxy_user", "The proxy user account name used when logging in",
       IN_SYSTEM_CHARSET);

static Sys_var_external_user Sys_external_user(
       "external_user", "The external user account used when logging in",
       IN_SYSTEM_CHARSET);

static Sys_var_ulong Sys_read_buff_size(
       "read_buffer_size",
       "Each thread that does a sequential scan allocates a buffer of "
       "this size for each table it scans. If you do many sequential scans, "
       "you may want to increase this value",
       SESSION_VAR(read_buff_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(IO_SIZE*2, INT_MAX32), DEFAULT(128*1024),
       BLOCK_SIZE(IO_SIZE));

static bool check_read_only(sys_var *self, THD *thd, set_var *var)
{
  /* Prevent self dead-lock */
  if (thd->locked_tables_mode || thd->in_active_multi_stmt_transaction())
  {
    my_error(ER_LOCK_OR_ACTIVE_TRANSACTION, MYF(0));
    return true;
  }
  return false;
}
static bool fix_read_only(sys_var *self, THD *thd, enum_var_type type)
{
  bool result= true;
  my_bool new_read_only= read_only; // make a copy before releasing a mutex
  DBUG_ENTER("sys_var_opt_readonly::update");

  if (read_only == FALSE || read_only == opt_readonly)
  {
    opt_readonly= read_only;
    DBUG_RETURN(false);
  }

  if (check_read_only(self, thd, 0)) // just in case
    goto end;

  if (thd->global_read_lock.is_acquired())
  {
    /*
      This connection already holds the global read lock.
      This can be the case with:
      - FLUSH TABLES WITH READ LOCK
      - SET GLOBAL READ_ONLY = 1
    */
    opt_readonly= read_only;
    DBUG_RETURN(false);
  }

  /*
    READ_ONLY=1 prevents write locks from being taken on tables and
    blocks transactions from committing. We therefore should make sure
    that no such events occur while setting the read_only variable.
    This is a 2 step process:
    [1] lock_global_read_lock()
      Prevents connections from obtaining new write locks on
      tables. Note that we can still have active rw transactions.
    [2] make_global_read_lock_block_commit()
      Prevents transactions from committing.
  */

  read_only= opt_readonly;
  mysql_mutex_unlock(&LOCK_global_system_variables);

  if (thd->global_read_lock.lock_global_read_lock(thd))
    goto end_with_mutex_unlock;

  if ((result= thd->global_read_lock.make_global_read_lock_block_commit(thd)))
    goto end_with_read_lock;

  /* Change the opt_readonly system variable, safe because the lock is held */
  opt_readonly= new_read_only;
  result= false;

 end_with_read_lock:
  /* Release the lock */
  thd->global_read_lock.unlock_global_read_lock(thd);
 end_with_mutex_unlock:
  mysql_mutex_lock(&LOCK_global_system_variables);
 end:
  read_only= opt_readonly;
  DBUG_RETURN(result);
}


static Sys_var_mybool Sys_readonly(
       "read_only",
       "Make all non-temporary tables read-only, with the exception for "
       "replication (slave) threads and users with the SUPER privilege",
       GLOBAL_VAR(read_only), CMD_LINE(OPT_ARG), DEFAULT(FALSE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_read_only), ON_UPDATE(fix_read_only));

// Small lower limit to be able to test MRR
static Sys_var_ulong Sys_read_rnd_buff_size(
       "read_rnd_buffer_size",
       "When reading rows in sorted order after a sort, the rows are read "
       "through this buffer to avoid a disk seeks",
       SESSION_VAR(read_rnd_buff_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, INT_MAX32), DEFAULT(256*1024), BLOCK_SIZE(1));

static Sys_var_ulong Sys_div_precincrement(
       "div_precision_increment", "Precision of the result of '/' "
       "operator will be increased on that value",
       SESSION_VAR(div_precincrement), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, DECIMAL_MAX_SCALE), DEFAULT(4), BLOCK_SIZE(1));

static Sys_var_uint Sys_eq_range_index_dive_limit(
       "eq_range_index_dive_limit",
       "The optimizer will use existing index statistics instead of "
       "doing index dives for equality ranges if the number of equality "
       "ranges for the index is larger than or equal to this number. "
       "If set to 0, index dives are always used.",
       SESSION_VAR(eq_range_index_dive_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX32), DEFAULT(10), BLOCK_SIZE(1));

static Sys_var_ulong Sys_range_alloc_block_size(
       "range_alloc_block_size",
       "Allocation block size for storing ranges during optimization",
       SESSION_VAR(range_alloc_block_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(RANGE_ALLOC_BLOCK_SIZE, ULONG_MAX),
       DEFAULT(RANGE_ALLOC_BLOCK_SIZE), BLOCK_SIZE(1024));

static Sys_var_ulong Sys_multi_range_count(
       "multi_range_count",
       "Number of key ranges to request at once. "
       "This variable has no effect, and is deprecated. "
       "It will be removed in a future release.",
       SESSION_VAR(multi_range_count), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, ULONG_MAX), DEFAULT(256), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0),
       DEPRECATED(""));

static bool fix_thd_mem_root(sys_var *self, THD *thd, enum_var_type type)
{
  if (type != OPT_GLOBAL)
    reset_root_defaults(thd->mem_root,
                        thd->variables.query_alloc_block_size,
                        thd->variables.query_prealloc_size);
  return false;
}
static Sys_var_ulong Sys_query_alloc_block_size(
       "query_alloc_block_size",
       "Allocation block size for query parsing and execution",
       SESSION_VAR(query_alloc_block_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, ULONG_MAX), DEFAULT(QUERY_ALLOC_BLOCK_SIZE),
       BLOCK_SIZE(1024), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_thd_mem_root));

static Sys_var_ulong Sys_query_prealloc_size(
       "query_prealloc_size",
       "Persistent buffer for query parsing and execution",
       SESSION_VAR(query_prealloc_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(QUERY_ALLOC_PREALLOC_SIZE, ULONG_MAX),
       DEFAULT(QUERY_ALLOC_PREALLOC_SIZE),
       BLOCK_SIZE(1024), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_thd_mem_root));

#ifdef HAVE_SMEM
static Sys_var_mybool Sys_shared_memory(
       "shared_memory", "Enable the shared memory",
       READ_ONLY GLOBAL_VAR(opt_enable_shared_memory), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

static Sys_var_charptr Sys_shared_memory_base_name(
       "shared_memory_base_name", "Base name of shared memory",
       READ_ONLY GLOBAL_VAR(shared_memory_base_name), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));
#endif

// this has to be NO_CMD_LINE as the command-line option has a different name
static Sys_var_mybool Sys_skip_external_locking(
       "skip_external_locking", "Don't use system (external) locking",
       READ_ONLY GLOBAL_VAR(my_disable_locking), NO_CMD_LINE, DEFAULT(TRUE));

static Sys_var_mybool Sys_skip_networking(
       "skip_networking", "Don't allow connection with TCP/IP",
       READ_ONLY GLOBAL_VAR(opt_disable_networking), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

static Sys_var_mybool Sys_skip_name_resolve(
       "skip_name_resolve",
       "Don't resolve hostnames. All hostnames are IP's or 'localhost'.",
       READ_ONLY GLOBAL_VAR(opt_skip_name_resolve),
       CMD_LINE(OPT_ARG, OPT_SKIP_RESOLVE),
       DEFAULT(FALSE));

static Sys_var_mybool Sys_skip_show_database(
       "skip_show_database", "Don't allow 'SHOW DATABASE' commands",
       READ_ONLY GLOBAL_VAR(opt_skip_show_db), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

static Sys_var_charptr Sys_socket(
       "socket", "Socket file to use for connection",
       READ_ONLY GLOBAL_VAR(mysqld_unix_port), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

/* 
  thread_concurrency is a no-op on all platforms since
  MySQL 5.1.  It will be removed in the context of
  WL#5265
*/
static Sys_var_ulong Sys_thread_concurrency(
       "thread_concurrency",
       "Permits the application to give the threads system a hint for "
       "the desired number of threads that should be run at the same time. "
       "This variable has no effect, and is deprecated. "
       "It will be removed in a future release. ",
       READ_ONLY GLOBAL_VAR(concurrency), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, 512), DEFAULT(DEFAULT_CONCURRENCY), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0), 
       DEPRECATED(""));

static Sys_var_ulong Sys_thread_stack(
       "thread_stack", "The stack size for each thread",
       READ_ONLY GLOBAL_VAR(my_thread_stack_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(128*1024, ULONG_MAX), DEFAULT(DEFAULT_THREAD_STACK),
       BLOCK_SIZE(1024));

static Sys_var_charptr Sys_tmpdir(
       "tmpdir", "Path for temporary files. Several paths may "
       "be specified, separated by a "
#if defined(__WIN__)
       "semicolon (;)"
#else
       "colon (:)"
#endif
       ", in this case they are used in a round-robin fashion",
       READ_ONLY GLOBAL_VAR(opt_mysql_tmpdir), CMD_LINE(REQUIRED_ARG, 't'),
       IN_FS_CHARSET, DEFAULT(0));

static bool fix_trans_mem_root(sys_var *self, THD *thd, enum_var_type type)
{
  if (type != OPT_GLOBAL)
    reset_root_defaults(&thd->transaction.mem_root,
                        thd->variables.trans_alloc_block_size,
                        thd->variables.trans_prealloc_size);
  return false;
}
static Sys_var_ulong Sys_trans_alloc_block_size(
       "transaction_alloc_block_size",
       "Allocation block size for transactions to be stored in binary log",
       SESSION_VAR(trans_alloc_block_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, ULONG_MAX), DEFAULT(QUERY_ALLOC_BLOCK_SIZE),
       BLOCK_SIZE(1024), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_trans_mem_root));

static Sys_var_ulong Sys_trans_prealloc_size(
       "transaction_prealloc_size",
       "Persistent buffer for transactions to be stored in binary log",
       SESSION_VAR(trans_prealloc_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, ULONG_MAX), DEFAULT(TRANS_ALLOC_PREALLOC_SIZE),
       BLOCK_SIZE(1024), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_trans_mem_root));

static const char *thread_handling_names[]=
{
  "one-thread-per-connection", "no-threads", "loaded-dynamically",
  0
};
static Sys_var_enum Sys_thread_handling(
       "thread_handling",
       "Define threads usage for handling queries, one of "
       "one-thread-per-connection, no-threads, loaded-dynamically"
       , READ_ONLY GLOBAL_VAR(thread_handling), CMD_LINE(REQUIRED_ARG),
       thread_handling_names, DEFAULT(0));

#ifdef HAVE_QUERY_CACHE
static bool fix_query_cache_size(sys_var *self, THD *thd, enum_var_type type)
{
  ulong new_cache_size= query_cache.resize(query_cache_size);
  /*
     Note: query_cache_size is a global variable reflecting the
     requested cache size. See also query_cache_size_arg
  */
  if (query_cache_size != new_cache_size)
    push_warning_printf(current_thd, Sql_condition::WARN_LEVEL_WARN,
                        ER_WARN_QC_RESIZE, ER(ER_WARN_QC_RESIZE),
                        query_cache_size, new_cache_size);

  query_cache_size= new_cache_size;
  return false;
}
static Sys_var_ulong Sys_query_cache_size(
       "query_cache_size",
       "The memory allocated to store results from old queries",
       GLOBAL_VAR(query_cache_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, ULONG_MAX), DEFAULT(1024U*1024U), BLOCK_SIZE(1024),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_query_cache_size));

static Sys_var_ulong Sys_query_cache_limit(
       "query_cache_limit",
       "Don't cache results that are bigger than this",
       GLOBAL_VAR(query_cache.query_cache_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, ULONG_MAX), DEFAULT(1024*1024), BLOCK_SIZE(1));

static bool fix_qcache_min_res_unit(sys_var *self, THD *thd, enum_var_type type)
{
  query_cache_min_res_unit=
    query_cache.set_min_res_unit(query_cache_min_res_unit);
  return false;
}
static Sys_var_ulong Sys_query_cache_min_res_unit(
       "query_cache_min_res_unit",
       "The minimum size for blocks allocated by the query cache",
       GLOBAL_VAR(query_cache_min_res_unit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, ULONG_MAX), DEFAULT(QUERY_CACHE_MIN_RESULT_DATA_SIZE),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_qcache_min_res_unit));

static const char *query_cache_type_names[]= { "OFF", "ON", "DEMAND", 0 };
static bool check_query_cache_type(sys_var *self, THD *thd, set_var *var)
{
  if (query_cache.is_disabled())
  {
    my_error(ER_QUERY_CACHE_DISABLED, MYF(0));
    return true;
  }
  return false;
}
static Sys_var_enum Sys_query_cache_type(
       "query_cache_type",
       "OFF = Don't cache or retrieve results. ON = Cache all results "
       "except SELECT SQL_NO_CACHE ... queries. DEMAND = Cache only "
       "SELECT SQL_CACHE ... queries",
       SESSION_VAR(query_cache_type), CMD_LINE(REQUIRED_ARG),
       query_cache_type_names, DEFAULT(0), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_query_cache_type));

static Sys_var_mybool Sys_query_cache_wlock_invalidate(
       "query_cache_wlock_invalidate",
       "Invalidate queries in query cache on LOCK for write",
       SESSION_VAR(query_cache_wlock_invalidate), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));
#endif /* HAVE_QUERY_CACHE */

static bool
on_check_opt_secure_auth(sys_var *self, THD *thd, set_var *var)
{
  if (!var->save_result.ulonglong_value)
  {
    WARN_DEPRECATED(thd, "pre-4.1 password hash", "post-4.1 password hash");
  }
  return false;
}

static Sys_var_mybool Sys_secure_auth(
       "secure_auth",
       "Disallow authentication for accounts that have old (pre-4.1) "
       "passwords",
       GLOBAL_VAR(opt_secure_auth), CMD_LINE(OPT_ARG, OPT_SECURE_AUTH),
       DEFAULT(TRUE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(on_check_opt_secure_auth)
       );

static Sys_var_charptr Sys_secure_file_priv(
       "secure_file_priv",
       "Limit LOAD DATA, SELECT ... OUTFILE, and LOAD_FILE() to files "
       "within specified directory",
       READ_ONLY GLOBAL_VAR(opt_secure_file_priv),
       CMD_LINE(REQUIRED_ARG), IN_FS_CHARSET, DEFAULT(0));

static bool fix_server_id(sys_var *self, THD *thd, enum_var_type type)
{
  server_id_supplied = 1;
  thd->server_id= server_id;
  return false;
}
static Sys_var_ulong Sys_server_id(
       "server_id",
       "Uniquely identifies the server instance in the community of "
       "replication partners",
       GLOBAL_VAR(server_id), CMD_LINE(REQUIRED_ARG, OPT_SERVER_ID),
       VALID_RANGE(0, UINT_MAX32), DEFAULT(0), BLOCK_SIZE(1), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(fix_server_id));

static Sys_var_charptr Sys_server_uuid(
       "server_uuid",
       "Uniquely identifies the server instance in the universe",
       READ_ONLY GLOBAL_VAR(server_uuid_ptr),
       NO_CMD_LINE, IN_FS_CHARSET, DEFAULT(server_uuid));

static Sys_var_uint Sys_server_id_bits(
       "server_id_bits",
       "Set number of significant bits in server-id",
       GLOBAL_VAR(opt_server_id_bits), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 32), DEFAULT(32), BLOCK_SIZE(1));

static Sys_var_mybool Sys_slave_compressed_protocol(
       "slave_compressed_protocol",
       "Use compression on master/slave protocol",
       GLOBAL_VAR(opt_slave_compressed_protocol), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

#ifdef HAVE_REPLICATION
static const char *slave_exec_mode_names[]=
       {"STRICT", "IDEMPOTENT", 0};
static Sys_var_enum Slave_exec_mode(
       "slave_exec_mode",
       "Modes for how replication events should be executed. Legal values "
       "are STRICT (default) and IDEMPOTENT. In IDEMPOTENT mode, "
       "replication will not stop for operations that are idempotent. "
       "In STRICT mode, replication will stop on any unexpected difference "
       "between the master and the slave",
       GLOBAL_VAR(slave_exec_mode_options), CMD_LINE(REQUIRED_ARG),
       slave_exec_mode_names, DEFAULT(SLAVE_EXEC_MODE_STRICT));
const char *slave_type_conversions_name[]=
       {"ALL_LOSSY", "ALL_NON_LOSSY", "ALL_UNSIGNED", "ALL_SIGNED", 0};
static Sys_var_set Slave_type_conversions(
       "slave_type_conversions",
       "Set of slave type conversions that are enabled. Legal values are:"
       " ALL_LOSSY to enable lossy conversions,"
       " ALL_NON_LOSSY to enable non-lossy conversions,"
       " ALL_UNSIGNED to treat all integer column type data to be unsigned values, and"
       " ALL_SIGNED to treat all integer column type data to be signed values."
       " Default treatment is ALL_SIGNED. If ALL_SIGNED and ALL_UNSIGNED both are"
       " specifed, ALL_SIGNED will take high priority than ALL_UNSIGNED."
       " If the variable is assigned the empty set, no conversions are"
       " allowed and it is expected that the types match exactly.",
       GLOBAL_VAR(slave_type_conversions_options), CMD_LINE(REQUIRED_ARG),
       slave_type_conversions_name,
       DEFAULT(0));

static Sys_var_mybool Sys_slave_sql_verify_checksum(
       "slave_sql_verify_checksum",
       "Force checksum verification of replication events after reading them "
       "from relay log. Note: Events are always checksum-verified by slave on "
       "receiving them from the network before writing them to the relay "
       "log. Enabled by default.",
       GLOBAL_VAR(opt_slave_sql_verify_checksum), CMD_LINE(OPT_ARG), DEFAULT(TRUE));

static bool slave_rows_search_algorithms_check(sys_var *self, THD *thd, set_var *var)
{
  String str, *res;
  /* null value is not allowed */
  if (check_not_null(self, thd, var))
    return true;

  res= var->value? var->value->val_str(&str) : NULL;
  if (res && res->is_empty())
    return true;

  return false;
}

static const char *slave_rows_search_algorithms_names[]= {"TABLE_SCAN", "INDEX_SCAN", "HASH_SCAN", 0};
static Sys_var_set Slave_rows_search_algorithms(
       "slave_rows_search_algorithms", 
       "Set of searching algorithms that the slave will use while "
       "searching for records from the storage engine to either "
       "updated or deleted them. Possible values are: INDEX_SCAN, "
       "TABLE_SCAN and HASH_SCAN. Any combination is allowed, and "
       "the slave will always pick the most suitable algorithm for "
       "any given scenario. "
       "(Default: INDEX_SCAN, TABLE_SCAN).",
       GLOBAL_VAR(slave_rows_search_algorithms_options), CMD_LINE(REQUIRED_ARG),
       slave_rows_search_algorithms_names,
       DEFAULT(SLAVE_ROWS_INDEX_SCAN | SLAVE_ROWS_TABLE_SCAN),  NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(slave_rows_search_algorithms_check), ON_UPDATE(NULL));
#endif

bool Sys_var_enum_binlog_checksum::global_update(THD *thd, set_var *var)
{
  bool check_purge= false;

  mysql_mutex_lock(mysql_bin_log.get_log_lock());
  if(mysql_bin_log.is_open())
  {
    bool alg_changed=
      (binlog_checksum_options != (uint) var->save_result.ulonglong_value);
    if (alg_changed)
      mysql_bin_log.checksum_alg_reset= (uint8) var->save_result.ulonglong_value;
    mysql_bin_log.rotate(true, &check_purge);
    if (alg_changed)
      mysql_bin_log.checksum_alg_reset= BINLOG_CHECKSUM_ALG_UNDEF; // done
  }
  else
  {
    binlog_checksum_options= var->save_result.ulonglong_value;
  }
  DBUG_ASSERT((ulong) binlog_checksum_options == var->save_result.ulonglong_value);
  DBUG_ASSERT(mysql_bin_log.checksum_alg_reset == BINLOG_CHECKSUM_ALG_UNDEF);
  mysql_mutex_unlock(mysql_bin_log.get_log_lock());
  
  if (check_purge)
    mysql_bin_log.purge();

  return 0;
}

static Sys_var_enum_binlog_checksum Binlog_checksum_enum(
       "binlog_checksum", "Type of BINLOG_CHECKSUM_ALG. Include checksum for "
       "log events in the binary log. Possible values are NONE and CRC32; "
       "default is CRC32.",
       GLOBAL_VAR(binlog_checksum_options), CMD_LINE(REQUIRED_ARG),
       binlog_checksum_type_names, DEFAULT(BINLOG_CHECKSUM_ALG_CRC32),
       NO_MUTEX_GUARD, NOT_IN_BINLOG);

static Sys_var_mybool Sys_master_verify_checksum(
       "master_verify_checksum",
       "Force checksum verification of logged events in binary log before "
       "sending them to slaves or printing them in output of SHOW BINLOG EVENTS. "
       "Disabled by default.",
       GLOBAL_VAR(opt_master_verify_checksum), CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_ulong Sys_slow_launch_time(
       "slow_launch_time",
       "If creating the thread takes longer than this value (in seconds), "
       "the Slow_launch_threads counter will be incremented",
       GLOBAL_VAR(slow_launch_time), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, LONG_TIMEOUT), DEFAULT(2), BLOCK_SIZE(1));

static Sys_var_ulong Sys_sort_buffer(
       "sort_buffer_size",
       "Each thread that needs to do a sort allocates a buffer of this size",
       SESSION_VAR(sortbuff_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(MIN_SORT_MEMORY, ULONG_MAX), DEFAULT(DEFAULT_SORT_MEMORY),
       BLOCK_SIZE(1));

export sql_mode_t expand_sql_mode(sql_mode_t sql_mode)
{
  if (sql_mode & MODE_ANSI)
  {
    /*
      Note that we dont set
      MODE_NO_KEY_OPTIONS | MODE_NO_TABLE_OPTIONS | MODE_NO_FIELD_OPTIONS
      to allow one to get full use of MySQL in this mode.

      MODE_ONLY_FULL_GROUP_BY was removed from ANSI mode because it is
      currently overly restrictive (see BUG#8510).
    */
    sql_mode|= (MODE_REAL_AS_FLOAT | MODE_PIPES_AS_CONCAT | MODE_ANSI_QUOTES |
                MODE_IGNORE_SPACE);
  }
  if (sql_mode & MODE_ORACLE)
    sql_mode|= (MODE_PIPES_AS_CONCAT | MODE_ANSI_QUOTES |
                MODE_IGNORE_SPACE |
                MODE_NO_KEY_OPTIONS | MODE_NO_TABLE_OPTIONS |
                MODE_NO_FIELD_OPTIONS | MODE_NO_AUTO_CREATE_USER);
  if (sql_mode & MODE_MSSQL)
    sql_mode|= (MODE_PIPES_AS_CONCAT | MODE_ANSI_QUOTES |
                MODE_IGNORE_SPACE |
                MODE_NO_KEY_OPTIONS | MODE_NO_TABLE_OPTIONS |
                MODE_NO_FIELD_OPTIONS);
  if (sql_mode & MODE_POSTGRESQL)
    sql_mode|= (MODE_PIPES_AS_CONCAT | MODE_ANSI_QUOTES |
                MODE_IGNORE_SPACE |
                MODE_NO_KEY_OPTIONS | MODE_NO_TABLE_OPTIONS |
                MODE_NO_FIELD_OPTIONS);
  if (sql_mode & MODE_DB2)
    sql_mode|= (MODE_PIPES_AS_CONCAT | MODE_ANSI_QUOTES |
                MODE_IGNORE_SPACE |
                MODE_NO_KEY_OPTIONS | MODE_NO_TABLE_OPTIONS |
                MODE_NO_FIELD_OPTIONS);
  if (sql_mode & MODE_MAXDB)
    sql_mode|= (MODE_PIPES_AS_CONCAT | MODE_ANSI_QUOTES |
                MODE_IGNORE_SPACE |
                MODE_NO_KEY_OPTIONS | MODE_NO_TABLE_OPTIONS |
                MODE_NO_FIELD_OPTIONS | MODE_NO_AUTO_CREATE_USER);
  if (sql_mode & MODE_MYSQL40)
    sql_mode|= MODE_HIGH_NOT_PRECEDENCE;
  if (sql_mode & MODE_MYSQL323)
    sql_mode|= MODE_HIGH_NOT_PRECEDENCE;
  if (sql_mode & MODE_TRADITIONAL)
    sql_mode|= (MODE_STRICT_TRANS_TABLES | MODE_STRICT_ALL_TABLES |
                MODE_NO_ZERO_IN_DATE | MODE_NO_ZERO_DATE |
                MODE_ERROR_FOR_DIVISION_BY_ZERO | MODE_NO_AUTO_CREATE_USER |
                MODE_NO_ENGINE_SUBSTITUTION);
  return sql_mode;
}
static bool check_sql_mode(sys_var *self, THD *thd, set_var *var)
{
  var->save_result.ulonglong_value=
    expand_sql_mode(var->save_result.ulonglong_value);
  return false;
}
static bool fix_sql_mode(sys_var *self, THD *thd, enum_var_type type)
{
  if (type != OPT_GLOBAL)
  {
    /* Update thd->server_status */
    if (thd->variables.sql_mode & MODE_NO_BACKSLASH_ESCAPES)
      thd->server_status|= SERVER_STATUS_NO_BACKSLASH_ESCAPES;
    else
      thd->server_status&= ~SERVER_STATUS_NO_BACKSLASH_ESCAPES;
  }
  return false;
}
/*
  WARNING: When adding new SQL modes don't forget to update the
  tables definitions that stores it's value (ie: mysql.event, mysql.proc)
*/
static const char *sql_mode_names[]=
{
  "REAL_AS_FLOAT", "PIPES_AS_CONCAT", "ANSI_QUOTES", "IGNORE_SPACE", ",",
  "ONLY_FULL_GROUP_BY", "NO_UNSIGNED_SUBTRACTION", "NO_DIR_IN_CREATE",
  "POSTGRESQL", "ORACLE", "MSSQL", "DB2", "MAXDB", "NO_KEY_OPTIONS",
  "NO_TABLE_OPTIONS", "NO_FIELD_OPTIONS", "MYSQL323", "MYSQL40", "ANSI",
  "NO_AUTO_VALUE_ON_ZERO", "NO_BACKSLASH_ESCAPES", "STRICT_TRANS_TABLES",
  "STRICT_ALL_TABLES", "NO_ZERO_IN_DATE", "NO_ZERO_DATE",
  "ALLOW_INVALID_DATES", "ERROR_FOR_DIVISION_BY_ZERO", "TRADITIONAL",
  "NO_AUTO_CREATE_USER", "HIGH_NOT_PRECEDENCE", "NO_ENGINE_SUBSTITUTION",
  "PAD_CHAR_TO_FULL_LENGTH",
  0
};
export bool sql_mode_string_representation(THD *thd, sql_mode_t sql_mode,
                                           LEX_STRING *ls)
{
  set_to_string(thd, ls, sql_mode, sql_mode_names);
  return ls->str == 0;
}
/*
  sql_mode should *not* be IN_BINLOG: even though it is written to the binlog,
  the slave ignores the MODE_NO_DIR_IN_CREATE variable, so slave's value
  differs from master's (see log_event.cc: Query_log_event::do_apply_event()).
*/
static Sys_var_set Sys_sql_mode(
       "sql_mode",
       "Syntax: sql-mode=mode[,mode[,mode...]]. See the manual for the "
       "complete list of valid sql modes",
       SESSION_VAR(sql_mode), CMD_LINE(REQUIRED_ARG),
       sql_mode_names, DEFAULT(MODE_NO_ENGINE_SUBSTITUTION), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(check_sql_mode), ON_UPDATE(fix_sql_mode));

#if defined(HAVE_OPENSSL) && !defined(EMBEDDED_LIBRARY)
#define SSL_OPT(X) CMD_LINE(REQUIRED_ARG,X)
#else
#define SSL_OPT(X) NO_CMD_LINE
#endif

static Sys_var_charptr Sys_ssl_ca(
       "ssl_ca",
       "CA file in PEM format (check OpenSSL docs, implies --ssl)",
       READ_ONLY GLOBAL_VAR(opt_ssl_ca), SSL_OPT(OPT_SSL_CA),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_ssl_capath(
       "ssl_capath",
       "CA directory (check OpenSSL docs, implies --ssl)",
       READ_ONLY GLOBAL_VAR(opt_ssl_capath), SSL_OPT(OPT_SSL_CAPATH),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_ssl_cert(
       "ssl_cert", "X509 cert in PEM format (implies --ssl)",
       READ_ONLY GLOBAL_VAR(opt_ssl_cert), SSL_OPT(OPT_SSL_CERT),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_ssl_cipher(
       "ssl_cipher", "SSL cipher to use (implies --ssl)",
       READ_ONLY GLOBAL_VAR(opt_ssl_cipher), SSL_OPT(OPT_SSL_CIPHER),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_ssl_key(
       "ssl_key", "X509 key in PEM format (implies --ssl)",
       READ_ONLY GLOBAL_VAR(opt_ssl_key), SSL_OPT(OPT_SSL_KEY),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_ssl_crl(
       "ssl_crl",
       "CRL file in PEM format (check OpenSSL docs, implies --ssl)",
       READ_ONLY GLOBAL_VAR(opt_ssl_crl), SSL_OPT(OPT_SSL_CRL),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_ssl_crlpath(
       "ssl_crlpath",
       "CRL directory (check OpenSSL docs, implies --ssl)",
       READ_ONLY GLOBAL_VAR(opt_ssl_crlpath), SSL_OPT(OPT_SSL_CRLPATH),
       IN_FS_CHARSET, DEFAULT(0));


// why ENUM and not BOOL ?
static const char *updatable_views_with_limit_names[]= {"NO", "YES", 0};
static Sys_var_enum Sys_updatable_views_with_limit(
       "updatable_views_with_limit",
       "YES = Don't issue an error message (warning only) if a VIEW without "
       "presence of a key of the underlying table is used in queries with a "
       "LIMIT clause for updating. NO = Prohibit update of a VIEW, which "
       "does not contain a key of the underlying table and the query uses "
       "a LIMIT clause (usually get from GUI tools)",
       SESSION_VAR(updatable_views_with_limit), CMD_LINE(REQUIRED_ARG),
       updatable_views_with_limit_names, DEFAULT(TRUE));

static Sys_var_mybool Sys_sync_frm(
       "sync_frm", "Sync .frm files to disk on creation",
       GLOBAL_VAR(opt_sync_frm), CMD_LINE(OPT_ARG),
       DEFAULT(TRUE));

static char *system_time_zone_ptr;
static Sys_var_charptr Sys_system_time_zone(
       "system_time_zone", "The server system time zone",
       READ_ONLY GLOBAL_VAR(system_time_zone_ptr), NO_CMD_LINE,
       IN_FS_CHARSET, DEFAULT(system_time_zone));

static Sys_var_ulong Sys_table_def_size(
       "table_definition_cache",
       "The number of cached table definitions",
       GLOBAL_VAR(table_def_size),
       CMD_LINE(REQUIRED_ARG, OPT_TABLE_DEFINITION_CACHE),
       VALID_RANGE(TABLE_DEF_CACHE_MIN, 512*1024),
       DEFAULT(TABLE_DEF_CACHE_DEFAULT),
       BLOCK_SIZE(1),
       NO_MUTEX_GUARD,
       NOT_IN_BINLOG,
       ON_CHECK(NULL),
       ON_UPDATE(NULL),
       NULL,
       /* table_definition_cache is used as a sizing hint by the performance schema. */
       sys_var::PARSE_EARLY);

static bool fix_table_cache_size(sys_var *self, THD *thd, enum_var_type type)
{
  /*
    table_open_cache parameter is a soft limit for total number of objects
    in all table cache instances. Once this value is updated we need to
    update value of a per-instance soft limit on table cache size.
  */
  table_cache_size_per_instance= table_cache_size / table_cache_instances;
  return false;
}

static Sys_var_ulong Sys_table_cache_size(
       "table_open_cache", "The number of cached open tables "
       "(total for all table cache instances)",
       GLOBAL_VAR(table_cache_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, 512*1024), DEFAULT(TABLE_OPEN_CACHE_DEFAULT),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(NULL),
       ON_UPDATE(fix_table_cache_size),
       NULL,
       /* table_open_cache is used as a sizing hint by the performance schema. */
       sys_var::PARSE_EARLY);

static Sys_var_ulong Sys_table_cache_instances(
       "table_open_cache_instances", "The number of table cache instances",
       READ_ONLY GLOBAL_VAR(table_cache_instances), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, Table_cache_manager::MAX_TABLE_CACHES), DEFAULT(1),
       BLOCK_SIZE(1), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(NULL),
       ON_UPDATE(NULL), NULL,
       /*
         table_open_cache is used as a sizing hint by the performance schema,
         and 'table_open_cache' is a prefix of 'table_open_cache_instances'.
         Is is better to keep these options together, to avoid confusing
         handle_options() with partial name matches.
       */
       sys_var::PARSE_EARLY);

static Sys_var_ulong Sys_thread_cache_size(
       "thread_cache_size",
       "How many threads we should keep in a cache for reuse",
       GLOBAL_VAR(max_blocked_pthreads),
       CMD_LINE(REQUIRED_ARG, OPT_THREAD_CACHE_SIZE),
       VALID_RANGE(0, 16384), DEFAULT(0), BLOCK_SIZE(1));

static bool check_tx_isolation(sys_var *self, THD *thd, set_var *var)
{
  if (var->type == OPT_DEFAULT && thd->in_active_multi_stmt_transaction())
  {
    DBUG_ASSERT(thd->in_multi_stmt_transaction_mode());
    my_error(ER_CANT_CHANGE_TX_CHARACTERISTICS, MYF(0));
    return TRUE;
  }
  return FALSE;
}


bool Sys_var_tx_isolation::session_update(THD *thd, set_var *var)
{
  if (var->type == OPT_SESSION && Sys_var_enum::session_update(thd, var))
    return TRUE;
  if (var->type == OPT_DEFAULT || !thd->in_active_multi_stmt_transaction())
  {
    /*
      Update the isolation level of the next transaction.
      I.e. if one did:
      COMMIT;
      SET SESSION ISOLATION LEVEL ...
      BEGIN; <-- this transaction has the new isolation
      Note, that in case of:
      COMMIT;
      SET TRANSACTION ISOLATION LEVEL ...
      SET SESSION ISOLATION LEVEL ...
      BEGIN; <-- the session isolation level is used, not the
      result of SET TRANSACTION statement.
     */
    thd->tx_isolation= (enum_tx_isolation) var->save_result.ulonglong_value;
  }
  return FALSE;
}


// NO_CMD_LINE - different name of the option
static Sys_var_tx_isolation Sys_tx_isolation(
       "tx_isolation", "Default transaction isolation level",
       SESSION_VAR(tx_isolation), NO_CMD_LINE,
       tx_isolation_names, DEFAULT(ISO_REPEATABLE_READ),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_tx_isolation));


static bool check_tx_read_only(sys_var *self, THD *thd, set_var *var)
{
  if (var->type == OPT_DEFAULT && thd->in_active_multi_stmt_transaction())
  {
    DBUG_ASSERT(thd->in_multi_stmt_transaction_mode());
    my_error(ER_CANT_CHANGE_TX_CHARACTERISTICS, MYF(0));
    return true;
  }
  return false;
}


bool Sys_var_tx_read_only::session_update(THD *thd, set_var *var)
{
  if (var->type == OPT_SESSION && Sys_var_mybool::session_update(thd, var))
    return true;
  if (var->type == OPT_DEFAULT || !thd->in_active_multi_stmt_transaction())
  {
    // @see Sys_var_tx_isolation::session_update() above for the rules.
    thd->tx_read_only= var->save_result.ulonglong_value;
  }
  return false;
}


static Sys_var_tx_read_only Sys_tx_read_only(
       "tx_read_only", "Set default transaction access mode to read only.",
       SESSION_VAR(tx_read_only), NO_CMD_LINE, DEFAULT(0),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_tx_read_only));

static Sys_var_ulonglong Sys_tmp_table_size(
       "tmp_table_size",
       "If an internal in-memory temporary table exceeds this size, MySQL "
       "will automatically convert it to an on-disk MyISAM table",
       SESSION_VAR(tmp_table_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, (ulonglong)~(intptr)0), DEFAULT(16*1024*1024),
       BLOCK_SIZE(1));

static Sys_var_mybool Sys_timed_mutexes(
       "timed_mutexes",
       "Specify whether to time mutexes (only InnoDB mutexes are currently "
       "supported)",
       GLOBAL_VAR(timed_mutexes), CMD_LINE(OPT_ARG), DEFAULT(0));

static char *server_version_ptr;
static Sys_var_charptr Sys_version(
       "version", "Server version",
       READ_ONLY GLOBAL_VAR(server_version_ptr), NO_CMD_LINE,
       IN_SYSTEM_CHARSET, DEFAULT(server_version));

static char *server_version_comment_ptr;
static Sys_var_charptr Sys_version_comment(
       "version_comment", "version_comment",
       READ_ONLY GLOBAL_VAR(server_version_comment_ptr), NO_CMD_LINE,
       IN_SYSTEM_CHARSET, DEFAULT(MYSQL_COMPILATION_COMMENT));

static char *server_version_compile_machine_ptr;
static Sys_var_charptr Sys_version_compile_machine(
       "version_compile_machine", "version_compile_machine",
       READ_ONLY GLOBAL_VAR(server_version_compile_machine_ptr), NO_CMD_LINE,
       IN_SYSTEM_CHARSET, DEFAULT(MACHINE_TYPE));

static char *server_version_compile_os_ptr;
static Sys_var_charptr Sys_version_compile_os(
       "version_compile_os", "version_compile_os",
       READ_ONLY GLOBAL_VAR(server_version_compile_os_ptr), NO_CMD_LINE,
       IN_SYSTEM_CHARSET, DEFAULT(SYSTEM_TYPE));

static Sys_var_ulong Sys_net_wait_timeout(
       "wait_timeout",
       "The number of seconds the server waits for activity on a "
       "connection before closing it",
       SESSION_VAR(net_wait_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, IF_WIN(INT_MAX32/1000, LONG_TIMEOUT)),
       DEFAULT(NET_WAIT_TIMEOUT), BLOCK_SIZE(1));

static Sys_var_plugin Sys_default_storage_engine(
       "default_storage_engine", "The default storage engine for new tables",
       SESSION_VAR(table_plugin), NO_CMD_LINE,
       MYSQL_STORAGE_ENGINE_PLUGIN, DEFAULT(&default_storage_engine),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_not_null));

static Sys_var_plugin Sys_default_tmp_storage_engine(
       "default_tmp_storage_engine", "The default storage engine for new explict temporary tables",
       SESSION_VAR(temp_table_plugin), NO_CMD_LINE,
       MYSQL_STORAGE_ENGINE_PLUGIN, DEFAULT(&default_tmp_storage_engine),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_not_null));

//  Alias for @@default_storage_engine
static Sys_var_plugin Sys_storage_engine(
       "storage_engine", "Alias for @@default_storage_engine. Deprecated",
       SESSION_VAR(table_plugin), NO_CMD_LINE,
       MYSQL_STORAGE_ENGINE_PLUGIN, DEFAULT(&default_storage_engine),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_not_null),
       ON_UPDATE(NULL), DEPRECATED("'@@default_storage_engine'"));

#if defined(ENABLED_DEBUG_SYNC)
/*
  Variable can be set for the session only.

  This could be changed later. Then we need to have a global array of
  actions in addition to the thread local ones. SET GLOBAL would
  manage the global array, SET [SESSION] the local array. A sync point
  would need to look for a local and a global action. Setting and
  executing of global actions need to be protected by a mutex.

  The purpose of global actions could be to allow synchronizing with
  connectionless threads that cannot execute SET statements.
*/
static Sys_var_debug_sync Sys_debug_sync(
       "debug_sync", "Debug Sync Facility",
       sys_var::ONLY_SESSION, NO_CMD_LINE,
       DEFAULT(0), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_has_super));
#endif /* defined(ENABLED_DEBUG_SYNC) */

static Sys_var_charptr Sys_date_format(
       "date_format", "The DATE format (ignored)",
       READ_ONLY GLOBAL_VAR(global_date_format.format.str),
       CMD_LINE(REQUIRED_ARG), IN_SYSTEM_CHARSET,
       DEFAULT(known_date_time_formats[ISO_FORMAT].date_format),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0),
       DEPRECATED(""));

static Sys_var_charptr Sys_datetime_format(
       "datetime_format", "The DATETIME format (ignored)",
       READ_ONLY GLOBAL_VAR(global_datetime_format.format.str),
       CMD_LINE(REQUIRED_ARG), IN_SYSTEM_CHARSET,
       DEFAULT(known_date_time_formats[ISO_FORMAT].datetime_format),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0),
       DEPRECATED(""));

static Sys_var_charptr Sys_time_format(
       "time_format", "The TIME format (ignored)",
       READ_ONLY GLOBAL_VAR(global_time_format.format.str),
       CMD_LINE(REQUIRED_ARG), IN_SYSTEM_CHARSET,
       DEFAULT(known_date_time_formats[ISO_FORMAT].time_format),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0),
       DEPRECATED(""));

static bool fix_autocommit(sys_var *self, THD *thd, enum_var_type type)
{
  if (type == OPT_GLOBAL)
  {
    if (global_system_variables.option_bits & OPTION_AUTOCOMMIT)
      global_system_variables.option_bits&= ~OPTION_NOT_AUTOCOMMIT;
    else
      global_system_variables.option_bits|= OPTION_NOT_AUTOCOMMIT;
    return false;
  }

  if (thd->variables.option_bits & OPTION_AUTOCOMMIT &&
      thd->variables.option_bits & OPTION_NOT_AUTOCOMMIT)
  { // activating autocommit

    if (trans_commit_stmt(thd) || trans_commit(thd))
    {
      thd->variables.option_bits&= ~OPTION_AUTOCOMMIT;
      return true;
    }
    /*
      Don't close thread tables or release metadata locks: if we do so, we
      risk releasing locks/closing tables of expressions used to assign
      other variables, as in:
      set @var=my_stored_function1(), @@autocommit=1, @var2=(select max(a)
      from my_table), ...
      The locks will be released at statement end anyway, as SET
      statement that assigns autocommit is marked to commit
      transaction implicitly at the end (@sa stmt_causes_implicitcommit()).
    */
    thd->variables.option_bits&=
                 ~(OPTION_BEGIN | OPTION_NOT_AUTOCOMMIT);
    thd->transaction.all.reset_unsafe_rollback_flags();
    thd->server_status|= SERVER_STATUS_AUTOCOMMIT;
    return false;
  }

  if (!(thd->variables.option_bits & OPTION_AUTOCOMMIT) &&
      !(thd->variables.option_bits & OPTION_NOT_AUTOCOMMIT))
  { // disabling autocommit

    thd->transaction.all.reset_unsafe_rollback_flags();
    thd->server_status&= ~SERVER_STATUS_AUTOCOMMIT;
    thd->variables.option_bits|= OPTION_NOT_AUTOCOMMIT;
    return false;
  }

  return false; // autocommit value wasn't changed
}
static Sys_var_bit Sys_autocommit(
       "autocommit", "autocommit",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_AUTOCOMMIT, DEFAULT(TRUE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(fix_autocommit));
export sys_var *Sys_autocommit_ptr= &Sys_autocommit; // for sql_yacc.yy

static Sys_var_mybool Sys_big_tables(
       "big_tables", "Allow big result sets by saving all "
       "temporary sets on file (Solves most 'table full' errors)",
       SESSION_VAR(big_tables), CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_bit Sys_big_selects(
       "sql_big_selects", "sql_big_selects",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_BIG_SELECTS,
       DEFAULT(FALSE));

static Sys_var_bit Sys_log_off(
       "sql_log_off", "sql_log_off",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_LOG_OFF,
       DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_has_super));

static bool fix_sql_log_bin_after_update(sys_var *self, THD *thd,
                                         enum_var_type type)
{
  if (type == OPT_SESSION)
  {
    if (thd->variables.sql_log_bin)
      thd->variables.option_bits |= OPTION_BIN_LOG;
    else
      thd->variables.option_bits &= ~OPTION_BIN_LOG;
  }
  return FALSE;
}

static bool check_sql_log_bin(sys_var *self, THD *thd, set_var *var)
{
  if (check_has_super(self, thd, var))
    return TRUE;

  if (var->type == OPT_GLOBAL)
    return FALSE;

  /* If in a stored function/trigger, it's too late to change sql_log_bin. */
  if (thd->in_sub_stmt)
  {
    my_error(ER_STORED_FUNCTION_PREVENTS_SWITCH_SQL_LOG_BIN, MYF(0));
    return TRUE;
  }
  /* Make the session variable 'sql_log_bin' read-only inside a transaction. */
  if (thd->in_active_multi_stmt_transaction())
  {
    my_error(ER_INSIDE_TRANSACTION_PREVENTS_SWITCH_SQL_LOG_BIN, MYF(0));
    return TRUE;
  }

  return FALSE;
}

static Sys_var_mybool Sys_log_binlog(
       "sql_log_bin", "sql_log_bin",
       SESSION_VAR(sql_log_bin), NO_CMD_LINE,
       DEFAULT(TRUE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_sql_log_bin),
       ON_UPDATE(fix_sql_log_bin_after_update));

static Sys_var_bit Sys_transaction_allow_batching(
       "transaction_allow_batching", "transaction_allow_batching",
       SESSION_ONLY(option_bits), NO_CMD_LINE, OPTION_ALLOW_BATCH,
       DEFAULT(FALSE));

static Sys_var_bit Sys_sql_warnings(
       "sql_warnings", "sql_warnings",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_WARNINGS,
       DEFAULT(FALSE));

static Sys_var_bit Sys_sql_notes(
       "sql_notes", "sql_notes",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_SQL_NOTES,
       DEFAULT(TRUE));

static Sys_var_bit Sys_auto_is_null(
       "sql_auto_is_null", "sql_auto_is_null",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_AUTO_IS_NULL,
       DEFAULT(FALSE), NO_MUTEX_GUARD, IN_BINLOG);

static Sys_var_bit Sys_safe_updates(
       "sql_safe_updates", "sql_safe_updates",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_SAFE_UPDATES,
       DEFAULT(FALSE));

static Sys_var_bit Sys_buffer_results(
       "sql_buffer_result", "sql_buffer_result",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_BUFFER_RESULT,
       DEFAULT(FALSE));

static Sys_var_bit Sys_quote_show_create(
       "sql_quote_show_create", "sql_quote_show_create",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_QUOTE_SHOW_CREATE,
       DEFAULT(TRUE));

static Sys_var_bit Sys_foreign_key_checks(
       "foreign_key_checks", "foreign_key_checks",
       SESSION_VAR(option_bits), NO_CMD_LINE,
       REVERSE(OPTION_NO_FOREIGN_KEY_CHECKS),
       DEFAULT(TRUE), NO_MUTEX_GUARD, IN_BINLOG);

static Sys_var_bit Sys_unique_checks(
       "unique_checks", "unique_checks",
       SESSION_VAR(option_bits), NO_CMD_LINE,
       REVERSE(OPTION_RELAXED_UNIQUE_CHECKS),
       DEFAULT(TRUE), NO_MUTEX_GUARD, IN_BINLOG);

#ifdef ENABLED_PROFILING
static Sys_var_bit Sys_profiling(
       "profiling", "profiling",
       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_PROFILING,
       DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(0), DEPRECATED(""));

static Sys_var_ulong Sys_profiling_history_size(
       "profiling_history_size", "Limit of query profiling memory",
       SESSION_VAR(profiling_history_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 100), DEFAULT(15), BLOCK_SIZE(1), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0), DEPRECATED(""));
#endif

static Sys_var_harows Sys_select_limit(
       "sql_select_limit",
       "The maximum number of rows to return from SELECT statements",
       SESSION_VAR(select_limit), NO_CMD_LINE,
       VALID_RANGE(0, HA_POS_ERROR), DEFAULT(HA_POS_ERROR), BLOCK_SIZE(1));

static bool update_timestamp(THD *thd, set_var *var)
{
  if (var->value)
  {
    double fl= floor(var->save_result.double_value); // Truncate integer part
    struct timeval tmp;
    tmp.tv_sec= (ulonglong) fl;
    /* Round nanoseconds to nearest microsecond */
    tmp.tv_usec= (ulonglong) rint((var->save_result.double_value - fl) * 1000000);
    thd->set_time(&tmp);
  }
  else // SET timestamp=DEFAULT
  {
    thd->user_time.tv_sec= 0;
    thd->user_time.tv_usec= 0;
  }
  return false;
}
static double read_timestamp(THD *thd)
{
  return (double) thd->start_time.tv_sec +
         (double) thd->start_time.tv_usec / 1000000;
}


static bool check_timestamp(sys_var *self, THD *thd, set_var *var)
{
  double val;

  if (!var->value)
    return FALSE;

  val= var->save_result.double_value;
  if (val != 0 &&          // this is how you set the default value
      (val < TIMESTAMP_MIN_VALUE || val > TIMESTAMP_MAX_VALUE))
  {
    ErrConvString prm(val);
    my_error(ER_WRONG_VALUE_FOR_VAR, MYF(0), "timestamp", prm.ptr());
    return TRUE;
  }
  return FALSE;
}


static Sys_var_session_special_double Sys_timestamp(
       "timestamp", "Set the time for this client",
       sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, 0), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_timestamp), 
       ON_UPDATE(update_timestamp), ON_READ(read_timestamp));

static bool update_last_insert_id(THD *thd, set_var *var)
{
  if (!var->value)
  {
    my_error(ER_NO_DEFAULT, MYF(0), var->var->name.str);
    return true;
  }
  thd->first_successful_insert_id_in_prev_stmt=
    var->save_result.ulonglong_value;
  return false;
}
static ulonglong read_last_insert_id(THD *thd)
{
  return (ulonglong) thd->read_first_successful_insert_id_in_prev_stmt();
}
static Sys_var_session_special Sys_last_insert_id(
       "last_insert_id", "The value to be returned from LAST_INSERT_ID()",
       sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, ULONGLONG_MAX), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_last_insert_id), ON_READ(read_last_insert_id));

// alias for last_insert_id(), Sybase-style
static Sys_var_session_special Sys_identity(
       "identity", "Synonym for the last_insert_id variable",
       sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, ULONGLONG_MAX), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_last_insert_id), ON_READ(read_last_insert_id));

/*
  insert_id should *not* be marked as written to the binlog (i.e., it
  should *not* be IN_BINLOG), because we want any statement that
  refers to insert_id explicitly to be unsafe.  (By "explicitly", we
  mean using @@session.insert_id, whereas insert_id is used
  "implicitly" when NULL value is inserted into an auto_increment
  column).

  We want statements referring explicitly to @@session.insert_id to be
  unsafe, because insert_id is modified internally by the slave sql
  thread when NULL values are inserted in an AUTO_INCREMENT column.
  This modification interfers with the value of the
  @@session.insert_id variable if @@session.insert_id is referred
  explicitly by an insert statement (as is seen by executing "SET
  @@session.insert_id=0; CREATE TABLE t (a INT, b INT KEY
  AUTO_INCREMENT); INSERT INTO t(a) VALUES (@@session.insert_id);" in
  statement-based logging mode: t will be different on master and
  slave).
*/
static bool update_insert_id(THD *thd, set_var *var)
{
  if (!var->value)
  {
    my_error(ER_NO_DEFAULT, MYF(0), var->var->name.str);
    return true;
  }
  thd->force_one_auto_inc_interval(var->save_result.ulonglong_value);
  return false;
}

static ulonglong read_insert_id(THD *thd)
{
  return thd->auto_inc_intervals_forced.minimum();
}
static Sys_var_session_special Sys_insert_id(
       "insert_id", "The value to be used by the following INSERT "
       "or ALTER TABLE statement when inserting an AUTO_INCREMENT value",
       sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, ULONGLONG_MAX), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_insert_id), ON_READ(read_insert_id));

static bool update_rand_seed1(THD *thd, set_var *var)
{
  if (!var->value)
  {
    my_error(ER_NO_DEFAULT, MYF(0), var->var->name.str);
    return true;
  }
  thd->rand.seed1= (ulong) var->save_result.ulonglong_value;
  return false;
}
static ulonglong read_rand_seed(THD *thd)
{
  return 0;
}
static Sys_var_session_special Sys_rand_seed1(
       "rand_seed1", "Sets the internal state of the RAND() "
       "generator for replication purposes",
       sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, ULONG_MAX), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_rand_seed1), ON_READ(read_rand_seed));

static bool update_rand_seed2(THD *thd, set_var *var)
{
  if (!var->value)
  {
    my_error(ER_NO_DEFAULT, MYF(0), var->var->name.str);
    return true;
  }
  thd->rand.seed2= (ulong) var->save_result.ulonglong_value;
  return false;
}
static Sys_var_session_special Sys_rand_seed2(
       "rand_seed2", "Sets the internal state of the RAND() "
       "generator for replication purposes",
       sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, ULONG_MAX), BLOCK_SIZE(1),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(update_rand_seed2), ON_READ(read_rand_seed));

static ulonglong read_error_count(THD *thd)
{
  return thd->get_stmt_da()->error_count();
}
// this really belongs to the SHOW STATUS
static Sys_var_session_special Sys_error_count(
       "error_count", "The number of errors that resulted from the "
       "last statement that generated messages",
       READ_ONLY sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, ULONGLONG_MAX), BLOCK_SIZE(1), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0), ON_READ(read_error_count));

static ulonglong read_warning_count(THD *thd)
{
  return thd->get_stmt_da()->warn_count();
}
// this really belongs to the SHOW STATUS
static Sys_var_session_special Sys_warning_count(
       "warning_count", "The number of errors, warnings, and notes "
       "that resulted from the last statement that generated messages",
       READ_ONLY sys_var::ONLY_SESSION, NO_CMD_LINE,
       VALID_RANGE(0, ULONGLONG_MAX), BLOCK_SIZE(1), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0), ON_READ(read_warning_count));

static Sys_var_ulong Sys_default_week_format(
       "default_week_format",
       "The default week format used by WEEK() functions",
       SESSION_VAR(default_week_format), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, 7), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_ulong Sys_group_concat_max_len(
       "group_concat_max_len",
       "The maximum length of the result of function  GROUP_CONCAT()",
       SESSION_VAR(group_concat_max_len), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(4, ULONG_MAX), DEFAULT(1024), BLOCK_SIZE(1));

static char *glob_hostname_ptr;
static Sys_var_charptr Sys_hostname(
       "hostname", "Server host name",
       READ_ONLY GLOBAL_VAR(glob_hostname_ptr), NO_CMD_LINE,
       IN_FS_CHARSET, DEFAULT(glob_hostname));

#ifndef EMBEDDED_LIBRARY
static Sys_var_charptr Sys_repl_report_host(
       "report_host",
       "Hostname or IP of the slave to be reported to the master during "
       "slave registration. Will appear in the output of SHOW SLAVE HOSTS. "
       "Leave unset if you do not want the slave to register itself with the "
       "master. Note that it is not sufficient for the master to simply read "
       "the IP of the slave off the socket once the slave connects. Due to "
       "NAT and other routing issues, that IP may not be valid for connecting "
       "to the slave from the master or other hosts",
       READ_ONLY GLOBAL_VAR(report_host), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_repl_report_user(
       "report_user",
       "The account user name of the slave to be reported to the master "
       "during slave registration",
       READ_ONLY GLOBAL_VAR(report_user), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_repl_report_password(
       "report_password",
       "The account password of the slave to be reported to the master "
       "during slave registration",
       READ_ONLY GLOBAL_VAR(report_password), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_uint Sys_repl_report_port(
       "report_port",
       "Port for connecting to slave reported to the master during slave "
       "registration. Set it only if the slave is listening on a non-default "
       "port or if you have a special tunnel from the master or other clients "
       "to the slave. If not sure, leave this option unset",
       READ_ONLY GLOBAL_VAR(report_port), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(0), BLOCK_SIZE(1));
#endif

static Sys_var_mybool Sys_keep_files_on_create(
       "keep_files_on_create",
       "Don't overwrite stale .MYD and .MYI even if no directory is specified",
       SESSION_VAR(keep_files_on_create), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE));

static char *license;
static Sys_var_charptr Sys_license(
       "license", "The type of license the server has",
       READ_ONLY GLOBAL_VAR(license), NO_CMD_LINE, IN_SYSTEM_CHARSET,
       DEFAULT(STRINGIFY_ARG(LICENSE)));

static bool check_log_path(sys_var *self, THD *thd, set_var *var)
{
  if (!var->value)
    return false; // DEFAULT is ok

  if (!var->save_result.string_value.str)
    return true;

  if (var->save_result.string_value.length > FN_REFLEN)
  { // path is too long
    my_error(ER_PATH_LENGTH, MYF(0), self->name.str);
    return true;
  }

  char path[FN_REFLEN];
  size_t path_length= unpack_filename(path, var->save_result.string_value.str);

  if (!path_length)
    return true;

  if (!is_filename_allowed(var->save_result.string_value.str, 
                           var->save_result.string_value.length, TRUE))
  {
     my_error(ER_WRONG_VALUE_FOR_VAR, MYF(0), 
              self->name.str, var->save_result.string_value.str);
     return true;
  }

  MY_STAT f_stat;

  if (my_stat(path, &f_stat, MYF(0)))
  {
    if (!MY_S_ISREG(f_stat.st_mode) || !(f_stat.st_mode & MY_S_IWRITE))
      return true; // not a regular writable file
    return false;
  }

  (void) dirname_part(path, var->save_result.string_value.str, &path_length);

  if (var->save_result.string_value.length - path_length >= FN_LEN)
  { // filename is too long
      my_error(ER_PATH_LENGTH, MYF(0), self->name.str);
      return true;
  }

  if (!path_length) // no path is good path (remember, relative to datadir)
    return false;

  if (my_access(path, (F_OK|W_OK)))
    return true; // directory is not writable

  return false;
}
static bool fix_log(char** logname, const char* default_logname,
                    const char*ext, bool enabled, void (*reopen)(char*))
{
  if (!*logname) // SET ... = DEFAULT
  {
    char buff[FN_REFLEN];
    *logname= my_strdup(make_log_name(buff, default_logname, ext),
                        MYF(MY_FAE+MY_WME));
    if (!*logname)
      return true;
  }
  logger.lock_exclusive();
  mysql_mutex_unlock(&LOCK_global_system_variables);
  if (enabled)
    reopen(*logname);
  logger.unlock();
  mysql_mutex_lock(&LOCK_global_system_variables);
  return false;
}
static void reopen_general_log(char* name)
{
  logger.get_log_file_handler()->close(0);
  logger.get_log_file_handler()->open_query_log(name);
}
static bool fix_general_log_file(sys_var *self, THD *thd, enum_var_type type)
{
  return fix_log(&opt_logname, default_logfile_name, ".log", opt_log,
                 reopen_general_log);
}
static Sys_var_charptr Sys_general_log_path(
       "general_log_file", "Log connections and queries to given file",
       GLOBAL_VAR(opt_logname), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_log_path), ON_UPDATE(fix_general_log_file));

static void reopen_slow_log(char* name)
{
  logger.get_slow_log_file_handler()->close(0);
  logger.get_slow_log_file_handler()->open_slow_log(name);
}
static bool fix_slow_log_file(sys_var *self, THD *thd, enum_var_type type)
{
  return fix_log(&opt_slow_logname, default_logfile_name, "-slow.log",
                 opt_slow_log, reopen_slow_log);
}
static Sys_var_charptr Sys_slow_log_path(
       "slow_query_log_file", "Log slow queries to given log file. "
       "Defaults logging to hostname-slow.log. Must be enabled to activate "
       "other slow log options",
       GLOBAL_VAR(opt_slow_logname), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_log_path), ON_UPDATE(fix_slow_log_file));

static Sys_var_have Sys_have_compress(
       "have_compress", "have_compress",
       READ_ONLY GLOBAL_VAR(have_compress), NO_CMD_LINE);

static Sys_var_have Sys_have_crypt(
       "have_crypt", "have_crypt",
       READ_ONLY GLOBAL_VAR(have_crypt), NO_CMD_LINE);

static Sys_var_have Sys_have_dlopen(
       "have_dynamic_loading", "have_dynamic_loading",
       READ_ONLY GLOBAL_VAR(have_dlopen), NO_CMD_LINE);

static Sys_var_have Sys_have_geometry(
       "have_geometry", "have_geometry",
       READ_ONLY GLOBAL_VAR(have_geometry), NO_CMD_LINE);

static Sys_var_have Sys_have_openssl(
       "have_openssl", "have_openssl",
       READ_ONLY GLOBAL_VAR(have_ssl), NO_CMD_LINE);

static Sys_var_have Sys_have_profiling(
       "have_profiling", "have_profiling",
       READ_ONLY GLOBAL_VAR(have_profiling), NO_CMD_LINE, NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(0), ON_UPDATE(0), DEPRECATED(""));

static Sys_var_have Sys_have_query_cache(
       "have_query_cache", "have_query_cache",
       READ_ONLY GLOBAL_VAR(have_query_cache), NO_CMD_LINE);

static Sys_var_have Sys_have_rtree_keys(
       "have_rtree_keys", "have_rtree_keys",
       READ_ONLY GLOBAL_VAR(have_rtree_keys), NO_CMD_LINE);

static Sys_var_have Sys_have_ssl(
       "have_ssl", "have_ssl",
       READ_ONLY GLOBAL_VAR(have_ssl), NO_CMD_LINE);

static Sys_var_have Sys_have_symlink(
       "have_symlink", "have_symlink",
       READ_ONLY GLOBAL_VAR(have_symlink), NO_CMD_LINE);

static bool fix_log_state(sys_var *self, THD *thd, enum_var_type type);
static Sys_var_mybool Sys_general_log(
       "general_log", "Log connections and queries to a table or log file. "
       "Defaults logging to a file hostname.log or a table mysql.general_log"
       "if --log-output=TABLE is used",
       GLOBAL_VAR(opt_log), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_log_state));

static Sys_var_mybool Sys_slow_query_log(
       "slow_query_log",
       "Log slow queries to a table or log file. Defaults logging to a file "
       "hostname-slow.log or a table mysql.slow_log if --log-output=TABLE is "
       "used. Must be enabled to activate other slow log options",
       GLOBAL_VAR(opt_slow_log), CMD_LINE(OPT_ARG),
       DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_log_state));


static bool fix_log_state(sys_var *self, THD *thd, enum_var_type type)
{
  bool res;
  my_bool *UNINIT_VAR(newvalptr), newval, UNINIT_VAR(oldval);
  uint UNINIT_VAR(log_type);

  if (self == &Sys_general_log)
  {
    newvalptr= &opt_log;
    oldval=    logger.get_log_file_handler()->is_open();
    log_type=  QUERY_LOG_GENERAL;
  }
  else if (self == &Sys_slow_query_log)
  {
    newvalptr= &opt_slow_log;
    oldval=    logger.get_slow_log_file_handler()->is_open();
    log_type=  QUERY_LOG_SLOW;
  }
  else
    DBUG_ASSERT(FALSE);

  newval= *newvalptr;
  if (oldval == newval)
    return false;

  *newvalptr= oldval; // [de]activate_log_handler works that way (sigh)

  mysql_mutex_unlock(&LOCK_global_system_variables);
  if (!newval)
  {
    logger.deactivate_log_handler(thd, log_type);
    res= false;
  }
  else
    res= logger.activate_log_handler(thd, log_type);
  mysql_mutex_lock(&LOCK_global_system_variables);
  return res;
}

static bool check_not_empty_set(sys_var *self, THD *thd, set_var *var)
{
  return var->save_result.ulonglong_value == 0;
}
static bool fix_log_output(sys_var *self, THD *thd, enum_var_type type)
{
  logger.lock_exclusive();
  logger.init_slow_log(log_output_options);
  logger.init_general_log(log_output_options);
  logger.unlock();
  return false;
}

static const char *log_output_names[] = { "NONE", "FILE", "TABLE", NULL};

static Sys_var_set Sys_log_output(
       "log_output", "Syntax: log-output=value[,value...], "
       "where \"value\" could be TABLE, FILE or NONE",
       GLOBAL_VAR(log_output_options), CMD_LINE(REQUIRED_ARG),
       log_output_names, DEFAULT(LOG_FILE), NO_MUTEX_GUARD, NOT_IN_BINLOG,
       ON_CHECK(check_not_empty_set), ON_UPDATE(fix_log_output));

#ifdef HAVE_REPLICATION
static Sys_var_mybool Sys_log_slave_updates(
       "log_slave_updates", "Tells the slave to log the updates from "
       "the slave thread to the binary log. You will need to turn it on if "
       "you plan to daisy-chain the slaves",
       READ_ONLY GLOBAL_VAR(opt_log_slave_updates), CMD_LINE(OPT_ARG),
       DEFAULT(0));

static Sys_var_charptr Sys_relay_log(
       "relay_log", "The location and name to use for relay logs",
       READ_ONLY GLOBAL_VAR(opt_relay_logname), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

/*
  Uses NO_CMD_LINE since the --relay-log-index option set
  opt_relaylog_index_name variable and computes a value for the
  relay_log_index variable.
*/
static Sys_var_charptr Sys_relay_log_index(
       "relay_log_index", "The location and name to use for the file "
       "that keeps a list of the last relay logs",
       READ_ONLY GLOBAL_VAR(relay_log_index), NO_CMD_LINE,
       IN_FS_CHARSET, DEFAULT(0));

/*
  Uses NO_CMD_LINE since the --log-bin-index option set
  opt_binlog_index_name variable and computes a value for the
  log_bin_index variable.
*/
static Sys_var_charptr Sys_binlog_index(
       "log_bin_index", "File that holds the names for last binary log files.",
       READ_ONLY GLOBAL_VAR(log_bin_index), NO_CMD_LINE,
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_relay_log_basename(
       "relay_log_basename",
       "The full path of the relay log file names, excluding the extension.",
       READ_ONLY GLOBAL_VAR(relay_log_basename), NO_CMD_LINE,
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_log_bin_basename(
       "log_bin_basename",
       "The full path of the binary log file names, excluding the extension.",
       READ_ONLY GLOBAL_VAR(log_bin_basename), NO_CMD_LINE,
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_charptr Sys_relay_log_info_file(
       "relay_log_info_file", "The location and name of the file that "
       "remembers where the SQL replication thread is in the relay logs",
       READ_ONLY GLOBAL_VAR(relay_log_info_file), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static Sys_var_mybool Sys_relay_log_purge(
       "relay_log_purge", "if disabled - do not purge relay logs. "
       "if enabled - purge them as soon as they are no more needed",
       GLOBAL_VAR(relay_log_purge), CMD_LINE(OPT_ARG), DEFAULT(TRUE));

static Sys_var_mybool Sys_relay_log_recovery(
       "relay_log_recovery", "Enables automatic relay log recovery "
       "right after the database startup, which means that the IO Thread "
       "starts re-fetching from the master right after the last transaction "
       "processed",
        READ_ONLY GLOBAL_VAR(relay_log_recovery), CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_mybool Sys_slave_allow_batching(
       "slave_allow_batching", "Allow slave to batch requests",
       GLOBAL_VAR(opt_slave_allow_batching),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE));

static Sys_var_charptr Sys_slave_load_tmpdir(
       "slave_load_tmpdir", "The location where the slave should put "
       "its temporary files when replicating a LOAD DATA INFILE command",
       READ_ONLY GLOBAL_VAR(slave_load_tmpdir), CMD_LINE(REQUIRED_ARG),
       IN_FS_CHARSET, DEFAULT(0));

static bool fix_slave_net_timeout(sys_var *self, THD *thd, enum_var_type type)
{
  DEBUG_SYNC(thd, "fix_slave_net_timeout");

  /*
   Here we have lock on LOCK_global_system_variables and we need
    lock on LOCK_active_mi. In START_SLAVE handler, we take these
    two locks in different order. This can lead to DEADLOCKs. See
    BUG#14236151 for more details.
   So we release lock on LOCK_global_system_variables before acquiring
    lock on LOCK_active_mi. But this could lead to isolation issues
    between multiple seters. Hence introducing secondary guard
    for this global variable and releasing the lock here and acquiring
    locks back again at the end of this function.
   */
  mysql_mutex_unlock(&LOCK_slave_net_timeout);
  mysql_mutex_unlock(&LOCK_global_system_variables);
  mysql_mutex_lock(&LOCK_active_mi);
  DBUG_PRINT("info", ("slave_net_timeout=%u mi->heartbeat_period=%.3f",
                     slave_net_timeout,
                     (active_mi ? active_mi->heartbeat_period : 0.0)));
  if (active_mi != NULL && slave_net_timeout < active_mi->heartbeat_period)
    push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,
                        ER_SLAVE_HEARTBEAT_VALUE_OUT_OF_RANGE_MAX,
                        ER(ER_SLAVE_HEARTBEAT_VALUE_OUT_OF_RANGE_MAX));
  mysql_mutex_unlock(&LOCK_active_mi);
  mysql_mutex_lock(&LOCK_global_system_variables);
  mysql_mutex_lock(&LOCK_slave_net_timeout);
  return false;
}
static PolyLock_mutex PLock_slave_net_timeout(&LOCK_slave_net_timeout);
static Sys_var_uint Sys_slave_net_timeout(
       "slave_net_timeout", "Number of seconds to wait for more data "
       "from a master/slave connection before aborting the read",
       GLOBAL_VAR(slave_net_timeout), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1, LONG_TIMEOUT), DEFAULT(SLAVE_NET_TIMEOUT), BLOCK_SIZE(1),
       &PLock_slave_net_timeout, NOT_IN_BINLOG, ON_CHECK(0),
       ON_UPDATE(fix_slave_net_timeout));

static bool check_slave_skip_counter(sys_var *self, THD *thd, set_var *var)
{
  bool result= false;
  mysql_mutex_lock(&LOCK_active_mi);
  if (active_mi != NULL)
  {
    mysql_mutex_lock(&active_mi->rli->run_lock);
    if (active_mi->rli->slave_running)
    {
      my_message(ER_SLAVE_MUST_STOP, ER(ER_SLAVE_MUST_STOP), MYF(0));
      result= true;
    }
    if (gtid_mode == 3)
    {
      my_message(ER_SQL_SLAVE_SKIP_COUNTER_NOT_SETTABLE_IN_GTID_MODE,
                 ER(ER_SQL_SLAVE_SKIP_COUNTER_NOT_SETTABLE_IN_GTID_MODE),
                 MYF(0));
      result= true;
    }
    mysql_mutex_unlock(&active_mi->rli->run_lock);
  }
  mysql_mutex_unlock(&LOCK_active_mi);
  return result;
}
static bool fix_slave_skip_counter(sys_var *self, THD *thd, enum_var_type type)
{

  /*
   To understand the below two unlock statments, please see comments in
    fix_slave_net_timeout function above
   */
  mysql_mutex_unlock(&LOCK_sql_slave_skip_counter);
  mysql_mutex_unlock(&LOCK_global_system_variables);
  mysql_mutex_lock(&LOCK_active_mi);
  if (active_mi != NULL)
  {
    mysql_mutex_lock(&active_mi->rli->run_lock);
    /*
      The following test should normally never be true as we test this
      in the check function;  To be safe against multiple
      SQL_SLAVE_SKIP_COUNTER request, we do the check anyway
    */
    if (!active_mi->rli->slave_running)
    {
      mysql_mutex_lock(&active_mi->rli->data_lock);
      active_mi->rli->slave_skip_counter= sql_slave_skip_counter;
      mysql_mutex_unlock(&active_mi->rli->data_lock);
    }
    mysql_mutex_unlock(&active_mi->rli->run_lock);
  }
  mysql_mutex_unlock(&LOCK_active_mi);
  mysql_mutex_lock(&LOCK_global_system_variables);
  mysql_mutex_lock(&LOCK_sql_slave_skip_counter);
  return 0;
}
static PolyLock_mutex PLock_sql_slave_skip_counter(&LOCK_sql_slave_skip_counter);
static Sys_var_uint Sys_slave_skip_counter(
       "sql_slave_skip_counter", "sql_slave_skip_counter",
       GLOBAL_VAR(sql_slave_skip_counter), NO_CMD_LINE,
       VALID_RANGE(0, UINT_MAX), DEFAULT(0), BLOCK_SIZE(1),
       &PLock_sql_slave_skip_counter, NOT_IN_BINLOG,
       ON_CHECK(check_slave_skip_counter), ON_UPDATE(fix_slave_skip_counter));

static Sys_var_charptr Sys_slave_skip_errors(
       "slave_skip_errors", "Tells the slave thread to continue "
       "replication when a query event returns an error from the "
       "provided list",
       READ_ONLY GLOBAL_VAR(opt_slave_skip_errors), CMD_LINE(REQUIRED_ARG),
       IN_SYSTEM_CHARSET, DEFAULT(0));

static Sys_var_ulonglong Sys_relay_log_space_limit(
       "relay_log_space_limit", "Maximum space to use for all relay logs",
       READ_ONLY GLOBAL_VAR(relay_log_space_limit), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, ULONG_MAX), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_uint Sys_sync_relaylog_period(
       "sync_relay_log", "Synchronously flush relay log to disk after "
       "every #th event. Use 0 to disable synchronous flushing",
       GLOBAL_VAR(sync_relaylog_period), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(10000), BLOCK_SIZE(1));

static Sys_var_uint Sys_sync_relayloginfo_period(
       "sync_relay_log_info", "Synchronously flush relay log info "
       "to disk after every #th transaction. Use 0 to disable "
       "synchronous flushing",
       GLOBAL_VAR(sync_relayloginfo_period), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(10000), BLOCK_SIZE(1));

static Sys_var_uint Sys_checkpoint_mts_period(
       "slave_checkpoint_period", "Gather workers' activities to "
       "Update progress status of Multi-threaded slave and flush "
       "the relay log info to disk after every #th milli-seconds.",
       GLOBAL_VAR(opt_mts_checkpoint_period), CMD_LINE(REQUIRED_ARG),
#ifndef DBUG_OFF
       VALID_RANGE(0, UINT_MAX), DEFAULT(300), BLOCK_SIZE(1));
#else
       VALID_RANGE(1, UINT_MAX), DEFAULT(300), BLOCK_SIZE(1));
#endif /* DBUG_OFF */

static Sys_var_uint Sys_checkpoint_mts_group(
       "slave_checkpoint_group",
       "Maximum number of processed transactions by Multi-threaded slave "
       "before a checkpoint operation is called to update progress status.",
       GLOBAL_VAR(opt_mts_checkpoint_group), CMD_LINE(REQUIRED_ARG),
#ifndef DBUG_OFF
       VALID_RANGE(1, MTS_MAX_BITS_IN_GROUP), DEFAULT(512), BLOCK_SIZE(1));
#else
       VALID_RANGE(32, MTS_MAX_BITS_IN_GROUP), DEFAULT(512), BLOCK_SIZE(8));
#endif /* DBUG_OFF */
#endif /* HAVE_REPLICATION */

static Sys_var_uint Sys_sync_binlog_period(
       "sync_binlog", "Synchronously flush binary log to disk after"
       " every #th write to the file. Use 0 (default) to disable synchronous"
       " flushing",
       GLOBAL_VAR(sync_binlog_period), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_uint Sys_sync_masterinfo_period(
       "sync_master_info", "Synchronously flush master info to disk "
       "after every #th event. Use 0 to disable synchronous flushing",
       GLOBAL_VAR(sync_masterinfo_period), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, UINT_MAX), DEFAULT(10000), BLOCK_SIZE(1));

#ifdef HAVE_REPLICATION
static Sys_var_ulong Sys_slave_trans_retries(
       "slave_transaction_retries", "Number of times the slave SQL "
       "thread will retry a transaction in case it failed with a deadlock "
       "or elapsed lock wait timeout, before giving up and stopping",
       GLOBAL_VAR(slave_trans_retries), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, ULONG_MAX), DEFAULT(10), BLOCK_SIZE(1));

static Sys_var_ulong Sys_slave_parallel_workers(
       "slave_parallel_workers",
       "Number of worker threads for executing events in parallel ",
       GLOBAL_VAR(opt_mts_slave_parallel_workers), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(0, MTS_MAX_WORKERS), DEFAULT(0), BLOCK_SIZE(1));

static Sys_var_ulonglong Sys_mts_pending_jobs_size_max(
       "slave_pending_jobs_size_max",
       "Max size of Slave Worker queues holding yet not applied events."
       "The least possible value must be not less than the master side "
       "max_allowed_packet.",
       GLOBAL_VAR(opt_mts_pending_jobs_size_max), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(1024, (ulonglong)~(intptr)0), DEFAULT(16 * 1024*1024),
       BLOCK_SIZE(1024), ON_CHECK(0));
#endif

static bool check_locale(sys_var *self, THD *thd, set_var *var)
{
  if (!var->value)
    return false;

  MY_LOCALE *locale;
  char buff[STRING_BUFFER_USUAL_SIZE];
  if (var->value->result_type() == INT_RESULT)
  {
    int lcno= (int)var->value->val_int();
    if (!(locale= my_locale_by_number(lcno)))
    {
      my_error(ER_UNKNOWN_LOCALE, MYF(0), llstr(lcno, buff));
      return true;
    }
    if (check_not_null(self, thd, var))
      return true;
  }
  else // STRING_RESULT
  {
    String str(buff, sizeof(buff), system_charset_info), *res;
    if (!(res=var->value->val_str(&str)))
      return true;
    else if (!(locale= my_locale_by_name(res->c_ptr_safe())))
    {
      ErrConvString err(res);
      my_error(ER_UNKNOWN_LOCALE, MYF(0), err.ptr());
      return true;
    }
  }

  var->save_result.ptr= locale;

  if (!locale->errmsgs->errmsgs)
  {
    mysql_mutex_lock(&LOCK_error_messages);
    if (!locale->errmsgs->errmsgs &&
        read_texts(ERRMSG_FILE, locale->errmsgs->language,
                   &locale->errmsgs->errmsgs,
                   ER_ERROR_LAST - ER_ERROR_FIRST + 1))
    {
      push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN, ER_UNKNOWN_ERROR,
                          "Can't process error message file for locale '%s'",
                          locale->name);
      mysql_mutex_unlock(&LOCK_error_messages);
      return true;
    }
    mysql_mutex_unlock(&LOCK_error_messages);
  }
  return false;
}
static Sys_var_struct Sys_lc_messages(
       "lc_messages", "Set the language used for the error messages",
       SESSION_VAR(lc_messages), NO_CMD_LINE,
       my_offsetof(MY_LOCALE, name), DEFAULT(&my_default_lc_messages),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_locale));

static Sys_var_struct Sys_lc_time_names(
       "lc_time_names", "Set the language used for the month "
       "names and the days of the week",
       SESSION_VAR(lc_time_names), NO_CMD_LINE,
       my_offsetof(MY_LOCALE, name), DEFAULT(&my_default_lc_time_names),
       NO_MUTEX_GUARD, IN_BINLOG, ON_CHECK(check_locale));

static Sys_var_tz Sys_time_zone(
       "time_zone", "time_zone",
       SESSION_VAR(time_zone), NO_CMD_LINE,
       DEFAULT(&default_tz), NO_MUTEX_GUARD, IN_BINLOG);

static bool fix_host_cache_size(sys_var *, THD *, enum_var_type)
{
  hostname_cache_resize((uint) host_cache_size);
  return false;
}

static Sys_var_ulong Sys_host_cache_size(
       "host_cache_size",
       "How many host names should be cached to avoid resolving.",
       GLOBAL_VAR(host_cache_size),
       CMD_LINE(REQUIRED_ARG, OPT_HOST_CACHE_SIZE), VALID_RANGE(0, 65536),
       DEFAULT(HOST_CACHE_SIZE),
       BLOCK_SIZE(1),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(NULL),
       ON_UPDATE(fix_host_cache_size));

static Sys_var_charptr Sys_ignore_db_dirs(
       "ignore_db_dirs",
       "The list of directories to ignore when collecting database lists",
       READ_ONLY GLOBAL_VAR(opt_ignore_db_dirs), 
       NO_CMD_LINE,
       IN_FS_CHARSET, DEFAULT(0));

/*
  This code is not being used but we will keep it as it may be
  useful if we decide to keeep enforce_gtid_consistency.
*/
#ifdef NON_DISABLED_GTID
static bool check_enforce_gtid_consistency(
  sys_var *self, THD *thd, set_var *var)
{
  DBUG_ENTER("check_enforce_gtid_consistency");

  my_error(ER_NOT_SUPPORTED_YET, MYF(0),
           "ENFORCE_GTID_CONSISTENCY");
  DBUG_RETURN(true);

  if (check_top_level_stmt_and_super(self, thd, var) ||
      check_outside_transaction(self, thd, var))
    DBUG_RETURN(true);
  if (gtid_mode >= 2 && var->value->val_int() == 0)
  {
    my_error(ER_GTID_MODE_2_OR_3_REQUIRES_ENFORCE_GTID_CONSISTENCY_ON, MYF(0));
    DBUG_RETURN(true);
  }
  DBUG_RETURN(false);
}
#endif

static Sys_var_mybool Sys_enforce_gtid_consistency(
       "enforce_gtid_consistency",
       "Prevents execution of statements that would be impossible to log "
       "in a transactionally safe manner. Currently, the disallowed "
       "statements include CREATE TEMPORARY TABLE inside transactions, "
       "all updates to non-transactional tables, and CREATE TABLE ... SELECT.",
       READ_ONLY GLOBAL_VAR(enforce_gtid_consistency),
       CMD_LINE(OPT_ARG), DEFAULT(FALSE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG
#ifdef NON_DISABLED_GTID
       , ON_CHECK(check_enforce_gtid_consistency));
#else
       );
#endif

static Sys_var_ulong Sys_sp_cache_size(
       "stored_program_cache",
       "The soft upper limit for number of cached stored routines for "
       "one connection.",
       GLOBAL_VAR(stored_program_cache_size), CMD_LINE(REQUIRED_ARG),
       VALID_RANGE(256, 512 * 1024), DEFAULT(256), BLOCK_SIZE(1));

static bool check_pseudo_slave_mode(sys_var *self, THD *thd, set_var *var)
{
  longlong previous_val= thd->variables.pseudo_slave_mode;
  longlong val= (longlong) var->save_result.ulonglong_value;
  bool rli_fake= false;

#ifndef EMBEDDED_LIBRARY
  rli_fake= thd->rli_fake ? true : false;
#endif

  if (rli_fake)
  {
    if (!val)
    {
#ifndef EMBEDDED_LIBRARY
      thd->rli_fake->end_info();
      delete thd->rli_fake;
      thd->rli_fake= NULL;
#endif
    }
    else if (previous_val && val)
      goto ineffective;
    else if (!previous_val && val)
      push_warning(thd, Sql_condition::WARN_LEVEL_WARN,
                   ER_WRONG_VALUE_FOR_VAR,
                   "'pseudo_slave_mode' is already ON.");
  }
  else
  {
    if (!previous_val && !val)
      goto ineffective;
    else if (previous_val && !val)
      push_warning(thd, Sql_condition::WARN_LEVEL_WARN,
                   ER_WRONG_VALUE_FOR_VAR,
                   "Slave applier execution mode not active, "
                   "statement ineffective.");
  }
  goto end;

ineffective:
  push_warning(thd, Sql_condition::WARN_LEVEL_WARN,
               ER_WRONG_VALUE_FOR_VAR,
               "'pseudo_slave_mode' change was ineffective.");

end:
  return FALSE;
}
static Sys_var_mybool Sys_pseudo_slave_mode(
       "pseudo_slave_mode",
       "SET pseudo_slave_mode= 0,1 are commands that mysqlbinlog "
       "adds to beginning and end of binary log dumps. While zero "
       "value indeed disables, the actual enabling of the slave "
       "applier execution mode is done implicitly when a "
       "Format_description_event is sent through the session.",
       SESSION_ONLY(pseudo_slave_mode), NO_CMD_LINE, DEFAULT(FALSE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_pseudo_slave_mode));


#ifdef HAVE_REPLICATION
static bool check_gtid_next(sys_var *self, THD *thd, set_var *var)
{
  DBUG_ENTER("check_gtid_next");

  // Note: we also check in sql_yacc.yy:set_system_variable that the
  // SET GTID_NEXT statement does not invoke a stored function.

  DBUG_PRINT("info", ("thd->in_sub_stmt=%d", thd->in_sub_stmt));

  // GTID_NEXT must be set by SUPER in a top-level statement
  if (check_top_level_stmt_and_super(self, thd, var))
    DBUG_RETURN(true);

  // check compatibility with GTID_NEXT
  const Gtid_set *gtid_next_list= thd->get_gtid_next_list_const();

  // Inside a transaction, GTID_NEXT is read-only if GTID_NEXT_LIST is
  // NULL.
  if (thd->in_active_multi_stmt_transaction() && gtid_next_list == NULL)
  {
    my_error(ER_CANT_CHANGE_GTID_NEXT_IN_TRANSACTION_WHEN_GTID_NEXT_LIST_IS_NULL, MYF(0));
    DBUG_RETURN(true);
  }

  // Read specification
  Gtid_specification spec;
  global_sid_lock->rdlock();
  if (spec.parse(global_sid_map, var->save_result.string_value.str) !=
      RETURN_STATUS_OK)
  {
    // fail on out of memory
    global_sid_lock->unlock();
    DBUG_RETURN(true);
  }
  global_sid_lock->unlock();

  // check compatibility with GTID_MODE
  if (gtid_mode == 0 && spec.type == GTID_GROUP)
    my_error(ER_CANT_SET_GTID_NEXT_TO_GTID_WHEN_GTID_MODE_IS_OFF, MYF(0));
  if (gtid_mode == 3 && spec.type == ANONYMOUS_GROUP)
    my_error(ER_CANT_SET_GTID_NEXT_TO_ANONYMOUS_WHEN_GTID_MODE_IS_ON, MYF(0));

  if (gtid_next_list != NULL)
  {
#ifdef HAVE_GTID_NEXT_LIST
    // If GTID_NEXT==SID:GNO, then SID:GNO must be listed in GTID_NEXT_LIST
    if (spec.type == GTID_GROUP && !gtid_next_list->contains_gtid(spec.gtid))
    {
      char buf[Gtid_specification::MAX_TEXT_LENGTH + 1];
      global_sid_lock->rdlock();
      spec.gtid.to_string(global_sid_map, buf);
      global_sid_lock->unlock();
      my_error(ER_GTID_NEXT_IS_NOT_IN_GTID_NEXT_LIST, MYF(0), buf);
      DBUG_RETURN(true);
    }

    // GTID_NEXT cannot be "AUTOMATIC" when GTID_NEXT_LIST != NULL.
    if (spec.type == AUTOMATIC_GROUP)
    {
      my_error(ER_GTID_NEXT_CANT_BE_AUTOMATIC_IF_GTID_NEXT_LIST_IS_NON_NULL,
               MYF(0));
      DBUG_RETURN(true);
    }
#else
    DBUG_ASSERT(0);
#endif
  }
  // check that we don't own a GTID
  else if(thd->owned_gtid.sidno != 0)
  {
    char buf[Gtid::MAX_TEXT_LENGTH + 1];
#ifndef DBUG_OFF
    DBUG_ASSERT(thd->owned_gtid.sidno > 0);
    global_sid_lock->wrlock();
    DBUG_ASSERT(gtid_state->get_owned_gtids()->
                thread_owns_anything(thd->thread_id));
#else
    global_sid_lock->rdlock();
#endif
    thd->owned_gtid.to_string(global_sid_map, buf);
    global_sid_lock->unlock();
    my_error(ER_CANT_SET_GTID_NEXT_WHEN_OWNING_GTID, MYF(0), buf);
    DBUG_RETURN(true);
  }

  DBUG_RETURN(false);
}

static bool update_gtid_next(sys_var *self, THD *thd, enum_var_type type)
{
  DBUG_ASSERT(type == OPT_SESSION);
  if (thd->variables.gtid_next.type == GTID_GROUP)
    return gtid_acquire_ownership_single(thd) != 0 ? true : false;
  return false;
}

#ifdef HAVE_GTID_NEXT_LIST
static bool check_gtid_next_list(sys_var *self, THD *thd, set_var *var)
{
  DBUG_ENTER("check_gtid_next_list");
  my_error(ER_NOT_SUPPORTED_YET, MYF(0), "GTID_NEXT_LIST");
  if (check_top_level_stmt_and_super(self, thd, var) ||
      check_outside_transaction(self, thd, var))
    DBUG_RETURN(true);
  if (gtid_mode == 0 && var->save_result.string_value.str != NULL)
    my_error(ER_CANT_SET_GTID_NEXT_LIST_TO_NON_NULL_WHEN_GTID_MODE_IS_OFF,
             MYF(0));
  DBUG_RETURN(false);
}

static bool update_gtid_next_list(sys_var *self, THD *thd, enum_var_type type)
{
  DBUG_ASSERT(type == OPT_SESSION);
  if (thd->get_gtid_next_list() != NULL)
    return gtid_acquire_ownership_multiple(thd) != 0 ? true : false;
  return false;
}

static Sys_var_gtid_set Sys_gtid_next_list(
       "gtid_next_list",
       "Before re-executing a transaction that contains multiple "
       "Global Transaction Identifiers, this variable must be set "
       "to the set of all re-executed transactions.",
       SESSION_ONLY(gtid_next_list), NO_CMD_LINE,
       DEFAULT(NULL), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(check_gtid_next_list),
       ON_UPDATE(update_gtid_next_list)
);
export sys_var *Sys_gtid_next_list_ptr= &Sys_gtid_next_list;
#endif

static Sys_var_gtid_specification Sys_gtid_next(
       "gtid_next",
       "Specified the Global Transaction Identifier for the following "
       "re-executed statement.",
       SESSION_ONLY(gtid_next), NO_CMD_LINE,
       DEFAULT("AUTOMATIC"), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(check_gtid_next), ON_UPDATE(update_gtid_next));
export sys_var *Sys_gtid_next_ptr= &Sys_gtid_next;

static Sys_var_gtid_executed Sys_gtid_executed(
       "gtid_executed",
       "The global variable contains the set of GTIDs in the "
       "binary log. The session variable contains the set of GTIDs "
       "in the current, ongoing transaction.");

static bool check_gtid_purged(sys_var *self, THD *thd, set_var *var)
{
  DBUG_ENTER("check_gtid_purged");

  if (!var->value || check_top_level_stmt(self, thd, var) ||
      check_outside_transaction(self, thd, var) ||
      check_outside_sp(self, thd, var))
    DBUG_RETURN(true);

  if (0 == gtid_mode)
  {
    my_error(ER_CANT_SET_GTID_PURGED_WHEN_GTID_MODE_IS_OFF, MYF(0));
    DBUG_RETURN(true);
  }

  if (var->value->result_type() != STRING_RESULT ||
      !var->save_result.string_value.str)
    DBUG_RETURN(true);

  DBUG_RETURN(false);
}

Gtid_set *gtid_purged;
static Sys_var_gtid_purged Sys_gtid_purged(
       "gtid_purged",
       "The set of GTIDs that existed in previous, purged binary logs.",
       GLOBAL_VAR(gtid_purged), NO_CMD_LINE,
       DEFAULT(NULL), NO_MUTEX_GUARD,
       NOT_IN_BINLOG, ON_CHECK(check_gtid_purged));
export sys_var *Sys_gtid_purged_ptr= &Sys_gtid_purged;

static Sys_var_gtid_owned Sys_gtid_owned(
       "gtid_owned",
       "The global variable lists all GTIDs owned by all threads. "
       "The session variable lists all GTIDs owned by the current thread.");

/*
  This code is not being used but we will keep it as it may be
  useful when we improve the code around Sys_gtid_mode.
*/
#ifdef NON_DISABLED_GTID
static bool check_gtid_mode(sys_var *self, THD *thd, set_var *var)
{
  DBUG_ENTER("check_gtid_mode");

  my_error(ER_NOT_SUPPORTED_YET, MYF(0), "GTID_MODE");
  DBUG_RETURN(true);

  if (check_top_level_stmt_and_super(self, thd, var) ||
      check_outside_transaction(self, thd, var))
    DBUG_RETURN(true);
  uint new_gtid_mode= var->value->val_int();
  if (abs((long)(new_gtid_mode - gtid_mode)) > 1)
  {
    my_error(ER_GTID_MODE_CAN_ONLY_CHANGE_ONE_STEP_AT_A_TIME, MYF(0));
    DBUG_RETURN(true);
  }
  if (new_gtid_mode >= 1)
  {
    if (!opt_bin_log || !opt_log_slave_updates)
    {
      my_error(ER_GTID_MODE_REQUIRES_BINLOG, MYF(0));
      DBUG_RETURN(false);
    }
  }
  if (new_gtid_mode >= 2)
  {
    /*
    if (new_gtid_mode == 3 &&
        (there are un-processed anonymous transactions in relay log ||
         there is a client executing an anonymous transaction))
    {
      my_error(ER_CANT_SET_GTID_MODE_3_WITH_UNPROCESSED_ANONYMOUS_GROUPS,
               MYF(0));
      DBUG_RETURN(true);
    }
    */
    if (!enforce_gtid_consistency)
    {
      //my_error(ER_GTID_MODE_2_OR_3_REQUIRES_ENFORCE_GTID_CONSISTENCY), MYF(0));
      DBUG_RETURN(true);
    }
  }
  else
  {
    /*
    if (new_gtid_mode == 0 &&
        (there are un-processed GTIDs in relay log ||
         there is a client executing a GTID transaction))
    {
      my_error(ER_CANT_SET_GTID_MODE_0_WITH_UNPROCESSED_GTID_GROUPS, MYF(0));
      DBUG_RETURN(true);
    }
    */
  }
  DBUG_RETURN(false);
}
#endif

static Sys_var_enum Sys_gtid_mode(
       "gtid_mode",
       /*
       "Whether Global Transaction Identifiers (GTIDs) are enabled: OFF, "
       "UPGRADE_STEP_1, UPGRADE_STEP_2, or ON. OFF means GTIDs are not "
       "supported at all, ON means GTIDs are supported by all servers in "
       "the replication topology. To safely switch from OFF to ON, first "
       "set all servers to UPGRADE_STEP_1, then set all servers to "
       "UPGRADE_STEP_2, then wait for all anonymous transactions to "
       "be re-executed on all servers, and finally set all servers to ON.",
       */
       "Whether Global Transaction Identifiers (GTIDs) are enabled. Can be "
       "ON or OFF.",
       READ_ONLY GLOBAL_VAR(gtid_mode), CMD_LINE(REQUIRED_ARG),
       gtid_mode_names, DEFAULT(GTID_MODE_OFF),
       NO_MUTEX_GUARD, NOT_IN_BINLOG
#ifdef NON_DISABLED_GTID
       , ON_CHECK(check_gtid_mode));
#else
       );
#endif

#endif // HAVE_REPLICATION


static Sys_var_mybool Sys_disconnect_on_expired_password(
       "disconnect_on_expired_password",
       "Give clients that don't signal password expiration support execution time error(s) instead of connection error",
       READ_ONLY GLOBAL_VAR(disconnect_on_expired_password),
       CMD_LINE(OPT_ARG), DEFAULT(TRUE));

#ifndef NO_EMBEDDED_ACCESS_CHECKS 
static Sys_var_mybool Sys_validate_user_plugins(
       "validate_user_plugins",
       "Turns on additional validation of authentication plugins assigned "
       "to user accounts. ",
       READ_ONLY NOT_VISIBLE GLOBAL_VAR(validate_user_plugins),
       CMD_LINE(OPT_ARG), DEFAULT(TRUE),
       NO_MUTEX_GUARD, NOT_IN_BINLOG);
#endif