filesort.cc

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/* Copyright (c) 2000, 2011, 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 "sql_priv.h"
#include "filesort.h"
#include "unireg.h"                      // REQUIRED by other includes
#ifdef HAVE_STDDEF_H
#include <stddef.h>                     /* for macro offsetof */
#endif
#include <m_ctype.h>
#include "sql_sort.h"
#include "probes_mysql.h"
#include "opt_range.h"                          // SQL_SELECT
#include "bounded_queue.h"
#include "filesort_utils.h"
#include "sql_select.h"
#include "debug_sync.h"
#include "opt_trace.h"
#include "sql_optimizer.h"              // JOIN

#include <algorithm>
#include <utility>
using std::max;
using std::min;

        /* functions defined in this file */

static uchar *read_buffpek_from_file(IO_CACHE *buffer_file, uint count,
                                     uchar *buf);
static ha_rows find_all_keys(Sort_param *param,SQL_SELECT *select,
                             Filesort_info *fs_info,
                             IO_CACHE *buffer_file,
                             IO_CACHE *tempfile,
                             Bounded_queue<uchar, uchar> *pq,
                             ha_rows *found_rows);
static int write_keys(Sort_param *param, Filesort_info *fs_info,
                      uint count, IO_CACHE *buffer_file, IO_CACHE *tempfile);
static void register_used_fields(Sort_param *param);
static int merge_index(Sort_param *param,uchar *sort_buffer,
                       BUFFPEK *buffpek,
                       uint maxbuffer,IO_CACHE *tempfile,
                       IO_CACHE *outfile);
static bool save_index(Sort_param *param, uint count,
                       Filesort_info *table_sort);
static uint suffix_length(ulong string_length);
static SORT_ADDON_FIELD *get_addon_fields(ulong max_length_for_sort_data,
                                          Field **ptabfield,
                                          uint sortlength, uint *plength);
static void unpack_addon_fields(struct st_sort_addon_field *addon_field,
                                uchar *buff);
static bool check_if_pq_applicable(Opt_trace_context *trace,
                                   Sort_param *param, Filesort_info *info,
                                   TABLE *table,
                                   ha_rows records, ulong memory_available);


void Sort_param::init_for_filesort(uint sortlen, TABLE *table,
                                   ulong max_length_for_sort_data,
                                   ha_rows maxrows, bool sort_positions)
{
  sort_length= sortlen;
  ref_length= table->file->ref_length;
  if (!(table->file->ha_table_flags() & HA_FAST_KEY_READ) &&
      !table->fulltext_searched && !sort_positions)
  {
    /* 
      Get the descriptors of all fields whose values are appended 
      to sorted fields and get its total length in addon_length.
    */
    addon_field= get_addon_fields(max_length_for_sort_data,
                                  table->field, sort_length, &addon_length);
  }
  if (addon_field)
    res_length= addon_length;
  else
  {
    res_length= ref_length;
    /* 
      The reference to the record is considered 
      as an additional sorted field
    */
    sort_length+= ref_length;
  }
  rec_length= sort_length + addon_length;
  max_rows= maxrows;
}


static void trace_filesort_information(Opt_trace_context *trace,
                                       const SORT_FIELD *sortorder,
                                       uint s_length)
{
  if (!trace->is_started())
    return;

  Opt_trace_array trace_filesort(trace, "filesort_information");
  for (; s_length-- ; sortorder++)
  {
    Opt_trace_object oto(trace);
    oto.add_alnum("direction", sortorder->reverse ? "desc" : "asc");

    if (sortorder->field)
    {
      if (strlen(sortorder->field->table->alias) != 0)
        oto.add_utf8_table(sortorder->field->table);
      else
        oto.add_alnum("table", "intermediate_tmp_table");
      oto.add_alnum("field", sortorder->field->field_name ?
                    sortorder->field->field_name : "tmp_table_column");
    }
    else
      oto.add("expression", sortorder->item);
  }
}


ha_rows filesort(THD *thd, TABLE *table, Filesort *filesort,
                 bool sort_positions, ha_rows *examined_rows,
                 ha_rows *found_rows)
{
  int error;
  ulong memory_available= thd->variables.sortbuff_size;
  uint maxbuffer;
  BUFFPEK *buffpek;
  ha_rows num_rows= HA_POS_ERROR;
  IO_CACHE tempfile, buffpek_pointers, *outfile; 
  Sort_param param;
  bool multi_byte_charset;
  Bounded_queue<uchar, uchar> pq;
  Opt_trace_context * const trace= &thd->opt_trace;
  SQL_SELECT *const select= filesort->select;
  ha_rows max_rows= filesort->limit;
  uint s_length= 0;

  DBUG_ENTER("filesort");

  if (!(s_length= filesort->make_sortorder()))
    DBUG_RETURN(HA_POS_ERROR);  /* purecov: inspected */

  /*
    We need a nameless wrapper, since we may be inside the "steps" of
    "join_execution".
  */
  Opt_trace_object trace_wrapper(trace);
  trace_filesort_information(trace, filesort->sortorder, s_length);

#ifdef SKIP_DBUG_IN_FILESORT
  DBUG_PUSH("");                /* No DBUG here */
#endif
  Item_subselect *subselect= table->reginfo.join_tab ?
     table->reginfo.join_tab->join->select_lex->master_unit()->item :
     NULL;

  MYSQL_FILESORT_START(table->s->db.str, table->s->table_name.str);
  DEBUG_SYNC(thd, "filesort_start");

  /*
   Release InnoDB's adaptive hash index latch (if holding) before
   running a sort.
  */
  ha_release_temporary_latches(thd);

  /* 
    Don't use table->sort in filesort as it is also used by 
    QUICK_INDEX_MERGE_SELECT. Work with a copy and put it back at the end 
    when index_merge select has finished with it.
  */
  Filesort_info table_sort= table->sort;
  table->sort.io_cache= NULL;
  DBUG_ASSERT(table_sort.record_pointers == NULL);
  
  outfile= table_sort.io_cache;
  my_b_clear(&tempfile);
  my_b_clear(&buffpek_pointers);
  buffpek=0;
  error= 1;

  param.init_for_filesort(sortlength(thd, filesort->sortorder, s_length,
                                     &multi_byte_charset),
                          table,
                          thd->variables.max_length_for_sort_data,
                          max_rows, sort_positions);

  table_sort.addon_buf= 0;
  table_sort.addon_length= param.addon_length;
  table_sort.addon_field= param.addon_field;
  table_sort.unpack= unpack_addon_fields;
  if (param.addon_field &&
      !(table_sort.addon_buf=
        (uchar *) my_malloc(param.addon_length, MYF(MY_WME))))
      goto err;

  if (select && select->quick)
    thd->inc_status_sort_range();
  else
    thd->inc_status_sort_scan();

  // If number of rows is not known, use as much of sort buffer as possible. 
  num_rows= table->file->estimate_rows_upper_bound();

  if (multi_byte_charset &&
      !(param.tmp_buffer= (char*) my_malloc(param.sort_length,MYF(MY_WME))))
    goto err;

  if (check_if_pq_applicable(trace, &param, &table_sort,
                             table, num_rows, memory_available))
  {
    DBUG_PRINT("info", ("filesort PQ is applicable"));
    const size_t compare_length= param.sort_length;
    if (pq.init(param.max_rows,
                true,                           // max_at_top
                NULL,                           // compare_function
                compare_length,
                &make_sortkey, &param, table_sort.get_sort_keys()))
    {
      /*
       If we fail to init pq, we have to give up:
       out of memory means my_malloc() will call my_error().
      */
      DBUG_PRINT("info", ("failed to allocate PQ"));
      table_sort.free_sort_buffer();
      DBUG_ASSERT(thd->is_error());
      goto err;
    }
    // For PQ queries (with limit) we initialize all pointers.
    table_sort.init_record_pointers();
    filesort->using_pq= true;
  }
  else
  {
    DBUG_PRINT("info", ("filesort PQ is not applicable"));

    const ulong min_sort_memory=
      max(MIN_SORT_MEMORY, param.sort_length * MERGEBUFF2);
    while (memory_available >= min_sort_memory)
    {
      ha_rows keys= memory_available / (param.rec_length + sizeof(char*));
      param.max_keys_per_buffer= (uint) min(num_rows, keys);
      if (table_sort.get_sort_keys())
      {
        // If we have already allocated a buffer, it better have same size!
        if (std::make_pair(param.max_keys_per_buffer, param.rec_length) !=
            table_sort.sort_buffer_properties())
        {
          /*
            table->sort will still have a pointer to the same buffer,
            but that will be overwritten by the assignment below.
          */
          table_sort.free_sort_buffer();
        }
      }
      table_sort.alloc_sort_buffer(param.max_keys_per_buffer, param.rec_length);
      if (table_sort.get_sort_keys())
        break;
      ulong old_memory_available= memory_available;
      memory_available= memory_available/4*3;
      if (memory_available < min_sort_memory &&
          old_memory_available > min_sort_memory)
        memory_available= min_sort_memory;
    }
    if (memory_available < min_sort_memory)
    {
      my_error(ER_OUT_OF_SORTMEMORY,MYF(ME_ERROR + ME_FATALERROR));
      goto err;
    }
  }

  if (open_cached_file(&buffpek_pointers,mysql_tmpdir,TEMP_PREFIX,
                       DISK_BUFFER_SIZE, MYF(MY_WME)))
    goto err;

  param.sort_form= table;
  param.end= (param.local_sortorder= filesort->sortorder) + s_length;
  // New scope, because subquery execution must be traced within an array.
  {
    Opt_trace_array ota(trace, "filesort_execution");
    num_rows= find_all_keys(&param, select,
                            &table_sort,
                            &buffpek_pointers,
                            &tempfile, 
                            pq.is_initialized() ? &pq : NULL,
                            found_rows);
    if (num_rows == HA_POS_ERROR)
      goto err;
  }

  maxbuffer= (uint) (my_b_tell(&buffpek_pointers)/sizeof(*buffpek));

  Opt_trace_object(trace, "filesort_summary")
    .add("rows", num_rows)
    .add("examined_rows", param.examined_rows)
    .add("number_of_tmp_files", maxbuffer)
    .add("sort_buffer_size", table_sort.sort_buffer_size())
    .add_alnum("sort_mode",
               param.addon_field ?
               "<sort_key, additional_fields>" : "<sort_key, rowid>");

  if (maxbuffer == 0)                   // The whole set is in memory
  {
    if (save_index(&param, (uint) num_rows, &table_sort))
      goto err;
  }
  else
  {
    /* filesort cannot handle zero-length records during merge. */
    DBUG_ASSERT(param.sort_length != 0);

    if (table_sort.buffpek && table_sort.buffpek_len < maxbuffer)
    {
      my_free(table_sort.buffpek);
      table_sort.buffpek= 0;
    }
    if (!(table_sort.buffpek=
          (uchar *) read_buffpek_from_file(&buffpek_pointers, maxbuffer,
                                 table_sort.buffpek)))
      goto err;
    buffpek= (BUFFPEK *) table_sort.buffpek;
    table_sort.buffpek_len= maxbuffer;
    close_cached_file(&buffpek_pointers);
        /* Open cached file if it isn't open */
    if (! my_b_inited(outfile) &&
        open_cached_file(outfile,mysql_tmpdir,TEMP_PREFIX,READ_RECORD_BUFFER,
                          MYF(MY_WME)))
      goto err;
    if (reinit_io_cache(outfile,WRITE_CACHE,0L,0,0))
      goto err;

    /*
      Use also the space previously used by string pointers in sort_buffer
      for temporary key storage.
    */
    param.max_keys_per_buffer= table_sort.sort_buffer_size() / param.rec_length;
    maxbuffer--;                                // Offset from 0
    if (merge_many_buff(&param,
                        (uchar*) table_sort.get_sort_keys(),
                        buffpek,&maxbuffer,
                        &tempfile))
      goto err;
    if (flush_io_cache(&tempfile) ||
        reinit_io_cache(&tempfile,READ_CACHE,0L,0,0))
      goto err;
    if (merge_index(&param,
                    (uchar*) table_sort.get_sort_keys(),
                    buffpek,
                    maxbuffer,
                    &tempfile,
                    outfile))
      goto err;
  }

  if (num_rows > param.max_rows)
  {
    // If find_all_keys() produced more results than the query LIMIT.
    num_rows= param.max_rows;
  }
  error= 0;

 err:
  my_free(param.tmp_buffer);
  if (!subselect || !subselect->is_uncacheable())
  {
    table_sort.free_sort_buffer();
    my_free(buffpek);
    table_sort.buffpek= 0;
    table_sort.buffpek_len= 0;
  }
  close_cached_file(&tempfile);
  close_cached_file(&buffpek_pointers);
  if (my_b_inited(outfile))
  {
    if (flush_io_cache(outfile))
      error=1;
    {
      my_off_t save_pos=outfile->pos_in_file;
      /* For following reads */
      if (reinit_io_cache(outfile,READ_CACHE,0L,0,0))
        error=1;
      outfile->end_of_file=save_pos;
    }
  }
  if (error)
  {
    int kill_errno= thd->killed_errno();
    DBUG_ASSERT(thd->is_error() || kill_errno);
    my_printf_error(ER_FILSORT_ABORT,
                    "%s: %s",
                    MYF(ME_ERROR + ME_WAITTANG),
                    ER_THD(thd, ER_FILSORT_ABORT),
                    kill_errno ?
                    ER(kill_errno) :
                    thd->get_stmt_da()->message());

    if (log_warnings > 1)
    {
      sql_print_warning("%s, host: %s, user: %s, thread: %lu, query: %-.4096s",
                        ER_THD(thd, ER_FILSORT_ABORT),
                        thd->security_ctx->host_or_ip,
                        &thd->security_ctx->priv_user[0],
                        (ulong) thd->thread_id,
                        thd->query());
    }
  }
  else
    thd->inc_status_sort_rows(num_rows);
  *examined_rows= param.examined_rows;
#ifdef SKIP_DBUG_IN_FILESORT
  DBUG_POP();                   /* Ok to DBUG */
#endif

  // Assign the copy back!
  table->sort= table_sort;

  DBUG_PRINT("exit",
             ("num_rows: %ld examined_rows: %ld found_rows: %ld",
              (long) num_rows, (long) *examined_rows, (long) *found_rows));
  MYSQL_FILESORT_DONE(error, num_rows);
  DBUG_RETURN(error ? HA_POS_ERROR : num_rows);
} /* filesort */


void filesort_free_buffers(TABLE *table, bool full)
{
  DBUG_ENTER("filesort_free_buffers");
  my_free(table->sort.record_pointers);
  table->sort.record_pointers= NULL;

  if (full)
  {
    table->sort.free_sort_buffer();
    my_free(table->sort.buffpek);
    table->sort.buffpek= NULL;
    table->sort.buffpek_len= 0;
  }

  my_free(table->sort.addon_buf);
  my_free(table->sort.addon_field);
  table->sort.addon_buf= NULL;
  table->sort.addon_field= NULL;
  DBUG_VOID_RETURN;
}

void Filesort::cleanup()
{
  if (select && own_select)
  {
    select->cleanup();
    select= NULL;
  }
}

uint Filesort::make_sortorder()
{
  uint count;
  SORT_FIELD *sort,*pos;
  ORDER *ord;
  DBUG_ENTER("make_sortorder");


  count=0;
  for (ord = order; ord; ord= ord->next)
    count++;
  if (!sortorder)
    sortorder= (SORT_FIELD*) sql_alloc(sizeof(SORT_FIELD) * (count + 1));
  pos= sort= sortorder;

  if (!pos)
    DBUG_RETURN(0);

  for (ord= order; ord; ord= ord->next, pos++)
  {
    Item *item= ord->item[0]->real_item();
    pos->field= 0; pos->item= 0;
    if (item->type() == Item::FIELD_ITEM)
      pos->field= ((Item_field*) item)->field;
    else if (item->type() == Item::SUM_FUNC_ITEM && !item->const_item())
      pos->field= ((Item_sum*) item)->get_tmp_table_field();
    else if (item->type() == Item::COPY_STR_ITEM)
    {                                           // Blob patch
      pos->item= ((Item_copy*) item)->get_item();
    }
    else
      pos->item= *ord->item;
    pos->reverse= (ord->direction == ORDER::ORDER_DESC);
    DBUG_ASSERT(pos->field != NULL || pos->item != NULL);
  }
  DBUG_RETURN(count);
}


static uchar *read_buffpek_from_file(IO_CACHE *buffpek_pointers, uint count,
                                     uchar *buf)
{
  ulong length= sizeof(BUFFPEK)*count;
  uchar *tmp= buf;
  DBUG_ENTER("read_buffpek_from_file");
  if (count > UINT_MAX/sizeof(BUFFPEK))
    return 0; /* sizeof(BUFFPEK)*count will overflow */
  if (!tmp)
    tmp= (uchar *)my_malloc(length, MYF(MY_WME));
  if (tmp)
  {
    if (reinit_io_cache(buffpek_pointers,READ_CACHE,0L,0,0) ||
        my_b_read(buffpek_pointers, (uchar*) tmp, length))
    {
      my_free(tmp);
      tmp=0;
    }
  }
  DBUG_RETURN(tmp);
}

#ifndef DBUG_OFF
/*
  Print a text, SQL-like record representation into dbug trace.

  Note: this function is a work in progress: at the moment
   - column read bitmap is ignored (can print garbage for unused columns)
   - there is no quoting
*/
static void dbug_print_record(TABLE *table, bool print_rowid)
{
  char buff[1024];
  Field **pfield;
  String tmp(buff,sizeof(buff),&my_charset_bin);
  DBUG_LOCK_FILE;
  
  fprintf(DBUG_FILE, "record (");
  for (pfield= table->field; *pfield ; pfield++)
    fprintf(DBUG_FILE, "%s%s", (*pfield)->field_name, (pfield[1])? ", ":"");
  fprintf(DBUG_FILE, ") = ");

  fprintf(DBUG_FILE, "(");
  for (pfield= table->field; *pfield ; pfield++)
  {
    Field *field=  *pfield;

    if (field->is_null())
      fwrite("NULL", sizeof(char), 4, DBUG_FILE);
   
    if (field->type() == MYSQL_TYPE_BIT)
      (void) field->val_int_as_str(&tmp, 1);
    else
      field->val_str(&tmp);

    fwrite(tmp.ptr(),sizeof(char),tmp.length(),DBUG_FILE);
    if (pfield[1])
      fwrite(", ", sizeof(char), 2, DBUG_FILE);
  }
  fprintf(DBUG_FILE, ")");
  if (print_rowid)
  {
    fprintf(DBUG_FILE, " rowid ");
    for (uint i=0; i < table->file->ref_length; i++)
    {
      fprintf(DBUG_FILE, "%x", (uchar)table->file->ref[i]);
    }
  }
  fprintf(DBUG_FILE, "\n");
  DBUG_UNLOCK_FILE;
}
#endif 

static ha_rows find_all_keys(Sort_param *param, SQL_SELECT *select,
                             Filesort_info *fs_info,
                             IO_CACHE *buffpek_pointers,
                             IO_CACHE *tempfile,
                             Bounded_queue<uchar, uchar> *pq,
                             ha_rows *found_rows)
{
  int error,flag,quick_select;
  uint idx,indexpos,ref_length;
  uchar *ref_pos,*next_pos,ref_buff[MAX_REFLENGTH];
  my_off_t record;
  TABLE *sort_form;
  THD *thd= current_thd;
  volatile THD::killed_state *killed= &thd->killed;
  handler *file;
  MY_BITMAP *save_read_set, *save_write_set;
  bool skip_record;

  DBUG_ENTER("find_all_keys");
  DBUG_PRINT("info",("using: %s",
                     (select ? select->quick ? "ranges" : "where":
                      "every row")));

  idx=indexpos=0;
  error=quick_select=0;
  sort_form=param->sort_form;
  file=sort_form->file;
  ref_length=param->ref_length;
  ref_pos= ref_buff;
  quick_select=select && select->quick;
  record=0;
  *found_rows= 0;
  flag= ((file->ha_table_flags() & HA_REC_NOT_IN_SEQ) || quick_select);
  if (flag)
    ref_pos= &file->ref[0];
  next_pos=ref_pos;
  if (!quick_select)
  {
    next_pos=(uchar*) 0;                        /* Find records in sequence */
    DBUG_EXECUTE_IF("bug14365043_1",
                    DBUG_SET("+d,ha_rnd_init_fail"););
    if ((error= file->ha_rnd_init(1)))
    {
      file->print_error(error, MYF(0));
      DBUG_RETURN(HA_POS_ERROR);
    }
    file->extra_opt(HA_EXTRA_CACHE,
                    current_thd->variables.read_buff_size);
  }

  if (quick_select)
  {
    if (select->quick->reset())
      DBUG_RETURN(HA_POS_ERROR);
  }

  /* Remember original bitmaps */
  save_read_set=  sort_form->read_set;
  save_write_set= sort_form->write_set;
  /* Set up temporary column read map for columns used by sort */
  bitmap_clear_all(&sort_form->tmp_set);
  /* Temporary set for register_used_fields and register_field_in_read_map */
  sort_form->read_set= &sort_form->tmp_set;
  // Include fields used for sorting in the read_set.
  register_used_fields(param); 

  // Include fields used by conditions in the read_set.
  if (select && select->cond)
    select->cond->walk(&Item::register_field_in_read_map, 1,
                       (uchar*) sort_form);

  // Include fields used by pushed conditions in the read_set.
  if (select && select->icp_cond)
    select->icp_cond->walk(&Item::register_field_in_read_map, 1,
                           (uchar*) sort_form);

  sort_form->column_bitmaps_set(&sort_form->tmp_set, &sort_form->tmp_set);

  for (;;)
  {
    if (quick_select)
    {
      if ((error= select->quick->get_next()))
        break;
      file->position(sort_form->record[0]);
      DBUG_EXECUTE_IF("debug_filesort", dbug_print_record(sort_form, TRUE););
    }
    else                                        /* Not quick-select */
    {
      {
        error= file->ha_rnd_next(sort_form->record[0]);
        if (!flag)
        {
          my_store_ptr(ref_pos,ref_length,record); // Position to row
          record+= sort_form->s->db_record_offset;
        }
        else if (!error)
          file->position(sort_form->record[0]);
      }
      if (error && error != HA_ERR_RECORD_DELETED)
        break;
    }

    if (*killed)
    {
      DBUG_PRINT("info",("Sort killed by user"));
      if (!quick_select)
      {
        (void) file->extra(HA_EXTRA_NO_CACHE);
        file->ha_rnd_end();
      }
      DBUG_RETURN(HA_POS_ERROR);                /* purecov: inspected */
    }
    if (error == 0)
      param->examined_rows++;
    if (!error && (!select ||
                   (!select->skip_record(thd, &skip_record) && !skip_record)))
    {
      ++(*found_rows);
      if (pq)
      {
        pq->push(ref_pos);
        idx= pq->num_elements();
      }
      else
      {
        if (idx == param->max_keys_per_buffer)
        {
          if (write_keys(param, fs_info, idx, buffpek_pointers, tempfile))
             DBUG_RETURN(HA_POS_ERROR);
          idx= 0;
          indexpos++;
        }
        make_sortkey(param, fs_info->get_record_buffer(idx++), ref_pos);
      }
    }
    /*
      Don't try unlocking the row if skip_record reported an error since in
      this case the transaction might have been rolled back already.
    */
    else if (!thd->is_error())
      file->unlock_row();
    /* It does not make sense to read more keys in case of a fatal error */
    if (thd->is_error())
      break;
  }
  if (!quick_select)
  {
    (void) file->extra(HA_EXTRA_NO_CACHE);      /* End cacheing of records */
    if (!next_pos)
      file->ha_rnd_end();
  }

  if (thd->is_error())
    DBUG_RETURN(HA_POS_ERROR);
  
  /* Signal we should use orignal column read and write maps */
  sort_form->column_bitmaps_set(save_read_set, save_write_set);

  DBUG_PRINT("test",("error: %d  indexpos: %d",error,indexpos));
  if (error != HA_ERR_END_OF_FILE)
  {
    file->print_error(error,MYF(ME_ERROR | ME_WAITTANG)); // purecov: inspected
    DBUG_RETURN(HA_POS_ERROR);                  /* purecov: inspected */
  }
  if (indexpos && idx &&
      write_keys(param, fs_info, idx, buffpek_pointers, tempfile))
    DBUG_RETURN(HA_POS_ERROR);                  /* purecov: inspected */
  const ha_rows retval= 
    my_b_inited(tempfile) ?
    (ha_rows) (my_b_tell(tempfile)/param->rec_length) : idx;
  DBUG_PRINT("info", ("find_all_keys return %u", (uint) retval));
  DBUG_RETURN(retval);
} /* find_all_keys */


static int
write_keys(Sort_param *param, Filesort_info *fs_info, uint count,
           IO_CACHE *buffpek_pointers, IO_CACHE *tempfile)
{
  size_t rec_length;
  uchar **end;
  BUFFPEK buffpek;
  DBUG_ENTER("write_keys");

  rec_length= param->rec_length;
  uchar **sort_keys= fs_info->get_sort_keys();

  fs_info->sort_buffer(param, count);

  if (!my_b_inited(tempfile) &&
      open_cached_file(tempfile, mysql_tmpdir, TEMP_PREFIX, DISK_BUFFER_SIZE,
                       MYF(MY_WME)))
    goto err;                                   /* purecov: inspected */
  /* check we won't have more buffpeks than we can possibly keep in memory */
  if (my_b_tell(buffpek_pointers) + sizeof(BUFFPEK) > (ulonglong)UINT_MAX)
    goto err;
  buffpek.file_pos= my_b_tell(tempfile);
  if ((ha_rows) count > param->max_rows)
    count=(uint) param->max_rows;               /* purecov: inspected */
  buffpek.count=(ha_rows) count;
  for (end=sort_keys+count ; sort_keys != end ; sort_keys++)
    if (my_b_write(tempfile, (uchar*) *sort_keys, (uint) rec_length))
      goto err;
  if (my_b_write(buffpek_pointers, (uchar*) &buffpek, sizeof(buffpek)))
    goto err;
  DBUG_RETURN(0);

err:
  DBUG_RETURN(1);
} /* write_keys */


static inline void store_length(uchar *to, uint length, uint pack_length)
{
  switch (pack_length) {
  case 1:
    *to= (uchar) length;
    break;
  case 2:
    mi_int2store(to, length);
    break;
  case 3:
    mi_int3store(to, length);
    break;
  default:
    mi_int4store(to, length);
    break;
  }
}


#ifdef WORDS_BIGENDIAN
const bool Is_big_endian= true;
#else
const bool Is_big_endian= false;
#endif
void copy_native_longlong(uchar *to, int to_length,
                          longlong val, bool is_unsigned)
{
  copy_integer<Is_big_endian>(to, to_length,
                              static_cast<uchar*>(static_cast<void*>(&val)),
                              sizeof(longlong),
                              is_unsigned);
}


void make_sortkey(Sort_param *param, uchar *to, uchar *ref_pos)
{
  SORT_FIELD *sort_field;

  for (sort_field= param->local_sortorder ;
       sort_field != param->end ;
       sort_field++)
  {
    bool maybe_null= false;
    if (sort_field->field)
    {
      Field *field= sort_field->field;
      if (field->maybe_null())
      {
        if (field->is_null())
        {
          if (sort_field->reverse)
            memset(to, 255, sort_field->length+1);
          else
            memset(to, 0, sort_field->length+1);
          to+= sort_field->length+1;
          continue;
        }
        else
          *to++=1;
      }
      field->make_sort_key(to, sort_field->length);
    }
    else
    {                                           // Item
      Item *item=sort_field->item;
      maybe_null= item->maybe_null;
      switch (sort_field->result_type) {
      case STRING_RESULT:
      {
        const CHARSET_INFO *cs=item->collation.collation;
        char fill_char= ((cs->state & MY_CS_BINSORT) ? (char) 0 : ' ');
        int diff;
        uint sort_field_length;

        if (maybe_null)
          *to++=1;
        /* All item->str() to use some extra byte for end null.. */
        String tmp((char*) to,sort_field->length+4,cs);
        String *res= item->str_result(&tmp);
        if (!res)
        {
          if (maybe_null)
            memset(to-1, 0, sort_field->length+1);
          else
          {
            /* purecov: begin deadcode */
            /*
              This should only happen during extreme conditions if we run out
              of memory or have an item marked not null when it can be null.
              This code is here mainly to avoid a hard crash in this case.
            */
            DBUG_ASSERT(0);
            DBUG_PRINT("warning",
                       ("Got null on something that shouldn't be null"));
            memset(to, 0, sort_field->length);  // Avoid crash
            /* purecov: end */
          }
          break;
        }
        uint length= res->length();
        sort_field_length= sort_field->length - sort_field->suffix_length;
        diff=(int) (sort_field_length - length);
        if (diff < 0)
        {
          diff=0;
          length= sort_field_length;
        }
        if (sort_field->suffix_length)
        {
          /* Store length last in result_string */
          store_length(to + sort_field_length, length,
                       sort_field->suffix_length);
        }
        if (sort_field->need_strxnfrm)
        {
          char *from=(char*) res->ptr();
          uint tmp_length;
          if ((uchar*) from == to)
          {
            set_if_smaller(length,sort_field->length);
            memcpy(param->tmp_buffer,from,length);
            from=param->tmp_buffer;
          }
          tmp_length= cs->coll->strnxfrm(cs, to, sort_field->length,
                                         item->max_char_length(),
                                         (uchar*) from, length,
                                         MY_STRXFRM_PAD_WITH_SPACE |
                                         MY_STRXFRM_PAD_TO_MAXLEN);
          DBUG_ASSERT(tmp_length == sort_field->length);
        }
        else
        {
          my_strnxfrm(cs,(uchar*)to,length,(const uchar*)res->ptr(),length);
          cs->cset->fill(cs, (char *)to+length,diff,fill_char);
        }
        break;
      }
      case INT_RESULT:
        {
          longlong value= item->field_type() == MYSQL_TYPE_TIME ?
                          item->val_time_temporal_result() :
                          item->is_temporal_with_date() ?
                          item->val_date_temporal_result() :
                          item->val_int_result();
          if (maybe_null)
          {
            *to++=1;                            /* purecov: inspected */
            if (item->null_value)
            {
              if (maybe_null)
                memset(to-1, 0, sort_field->length+1);
              else
              {
                DBUG_PRINT("warning",
                           ("Got null on something that shouldn't be null"));
                memset(to, 0, sort_field->length);
              }
              break;
            }
          }
          copy_native_longlong(to, sort_field->length,
                               value, item->unsigned_flag);
          break;
        }
      case DECIMAL_RESULT:
        {
          my_decimal dec_buf, *dec_val= item->val_decimal_result(&dec_buf);
          if (maybe_null)
          {
            if (item->null_value)
            { 
              memset(to, 0, sort_field->length+1);
              to++;
              break;
            }
            *to++=1;
          }
          if (sort_field->length < DECIMAL_MAX_FIELD_SIZE)
          {
            uchar buf[DECIMAL_MAX_FIELD_SIZE];
            my_decimal2binary(E_DEC_FATAL_ERROR, dec_val, buf,
                              item->max_length - (item->decimals ? 1:0),
                              item->decimals);
            memcpy(to, buf, sort_field->length);
          }
          else
          {
            my_decimal2binary(E_DEC_FATAL_ERROR, dec_val, to,
                              item->max_length - (item->decimals ? 1:0),
                              item->decimals);
          }
         break;
        }
      case REAL_RESULT:
        {
          double value= item->val_result();
          if (maybe_null)
          {
            if (item->null_value)
            {
              memset(to, 0, sort_field->length+1);
              to++;
              break;
            }
            *to++=1;
          }
          if (sort_field->length < sizeof(double))
          {
            uchar buf[sizeof(double)];
            change_double_for_sort(value, buf);
            memcpy(to, buf, sort_field->length);
          }
          else
          {
            change_double_for_sort(value, (uchar*) to);
          }
          break;
        }
      case ROW_RESULT:
      default: 
        // This case should never be choosen
        DBUG_ASSERT(0);
        break;
      }
    }
    if (sort_field->reverse)
    {                                                   /* Revers key */
      if (maybe_null)
        to[-1]= ~to[-1];
      uint length= sort_field->length;
      while (length--)
      {
        *to = (uchar) (~ *to);
        to++;
      }
    }
    else
      to+= sort_field->length;
  }

  if (param->addon_field)
  {
    /* 
      Save field values appended to sorted fields.
      First null bit indicators are appended then field values follow.
      In this implementation we use fixed layout for field values -
      the same for all records.
    */
    SORT_ADDON_FIELD *addonf= param->addon_field;
    uchar *nulls= to;
    DBUG_ASSERT(addonf != 0);
    memset(nulls, 0, addonf->offset);
    to+= addonf->offset;
    for (Field* field; (field= addonf->field) ; addonf++)
    {
      if (addonf->null_bit && field->is_null())
      {
        nulls[addonf->null_offset]|= addonf->null_bit;
      }
      else
      {
        (void) field->pack(to, field->ptr);
      }
      to+= addonf->length;
    }
  }
  else
  {
    /* Save filepos last */
    memcpy((uchar*) to, ref_pos, (size_t) param->ref_length);
  }
  return;
}


/*
  Register fields used by sorting in the sorted table's read set
*/

static void register_used_fields(Sort_param *param)
{
  reg1 SORT_FIELD *sort_field;
  TABLE *table=param->sort_form;
  MY_BITMAP *bitmap= table->read_set;

  for (sort_field= param->local_sortorder ;
       sort_field != param->end ;
       sort_field++)
  {
    Field *field;
    if ((field= sort_field->field))
    {
      if (field->table == table)
      bitmap_set_bit(bitmap, field->field_index);
    }
    else
    {                                           // Item
      sort_field->item->walk(&Item::register_field_in_read_map, 1,
                             (uchar *) table);
    }
  }

  if (param->addon_field)
  {
    SORT_ADDON_FIELD *addonf= param->addon_field;
    Field *field;
    for ( ; (field= addonf->field) ; addonf++)
      bitmap_set_bit(bitmap, field->field_index);
  }
  else
  {
    /* Save filepos last */
    table->prepare_for_position();
  }
}

static bool save_index(Sort_param *param, uint count, Filesort_info *table_sort)
{
  uint offset,res_length;
  uchar *to;
  DBUG_ENTER("save_index");

  table_sort->sort_buffer(param, count);
  res_length= param->res_length;
  offset= param->rec_length-res_length;
  if (!(to= table_sort->record_pointers= 
        (uchar*) my_malloc(res_length*count, MYF(MY_WME))))
    DBUG_RETURN(1);                 /* purecov: inspected */
  uchar **sort_keys= table_sort->get_sort_keys();
  for (uchar **end= sort_keys+count ; sort_keys != end ; sort_keys++)
  {
    memcpy(to, *sort_keys+offset, res_length);
    to+= res_length;
  }
  DBUG_RETURN(0);
}


bool check_if_pq_applicable(Opt_trace_context *trace,
                            Sort_param *param,
                            Filesort_info *filesort_info,
                            TABLE *table, ha_rows num_rows,
                            ulong memory_available)
{
  DBUG_ENTER("check_if_pq_applicable");

  /*
    How much Priority Queue sort is slower than qsort.
    Measurements (see unit test) indicate that PQ is roughly 3 times slower.
  */
  const double PQ_slowness= 3.0;

  Opt_trace_object trace_filesort(trace,
                                  "filesort_priority_queue_optimization");
  if (param->max_rows == HA_POS_ERROR)
  {
    trace_filesort
      .add("usable", false)
      .add_alnum("cause", "not applicable (no LIMIT)");
    DBUG_RETURN(false);
  }

  trace_filesort
    .add("limit", param->max_rows)
    .add("rows_estimate", num_rows)
    .add("row_size", param->rec_length)
    .add("memory_available", memory_available);

  if (param->max_rows + 2 >= UINT_MAX)
  {
    trace_filesort.add("usable", false).add_alnum("cause", "limit too large");
    DBUG_RETURN(false);
  }

  ulong num_available_keys=
    memory_available / (param->rec_length + sizeof(char*));
  // We need 1 extra record in the buffer, when using PQ.
  param->max_keys_per_buffer= (uint) param->max_rows + 1;

  if (num_rows < num_available_keys)
  {
    // The whole source set fits into memory.
    if (param->max_rows < num_rows/PQ_slowness )
    {
      filesort_info->alloc_sort_buffer(param->max_keys_per_buffer,
                                       param->rec_length);
      trace_filesort.add("chosen", true);
      DBUG_RETURN(filesort_info->get_sort_keys() != NULL);
    }
    else
    {
      // PQ will be slower.
      trace_filesort.add("chosen", false)
        .add_alnum("cause", "quicksort_is_cheaper");
      DBUG_RETURN(false);
    }
  }

  // Do we have space for LIMIT rows in memory?
  if (param->max_keys_per_buffer < num_available_keys)
  {
    filesort_info->alloc_sort_buffer(param->max_keys_per_buffer,
                                     param->rec_length);
    trace_filesort.add("chosen", true);
    DBUG_RETURN(filesort_info->get_sort_keys() != NULL);
  }

  // Try to strip off addon fields.
  if (param->addon_field)
  {
    const ulong row_length=
      param->sort_length + param->ref_length + sizeof(char*);
    num_available_keys= memory_available / row_length;

    Opt_trace_object trace_addon(trace, "strip_additional_fields");
    trace_addon.add("row_size", row_length);

    // Can we fit all the keys in memory?
    if (param->max_keys_per_buffer >= num_available_keys)
    {
      trace_addon.add("chosen", false).add_alnum("cause", "not_enough_space");
    }
    else
    {
      const double sort_merge_cost=
        get_merge_many_buffs_cost_fast(num_rows,
                                       num_available_keys,
                                       row_length);
      trace_addon.add("sort_merge_cost", sort_merge_cost);
      /*
        PQ has cost:
        (insert + qsort) * log(queue size) * ROWID_COMPARE_COST +
        cost of file lookup afterwards.
        The lookup cost is a bit pessimistic: we take scan_time and assume
        that on average we find the row after scanning half of the file.
        A better estimate would be lookup cost, but note that we are doing
        random lookups here, rather than sequential scan.
      */
      const double pq_cpu_cost= 
        (PQ_slowness * num_rows + param->max_keys_per_buffer) *
        log((double) param->max_keys_per_buffer) * ROWID_COMPARE_COST;
      const double pq_io_cost=
        param->max_rows * table->file->scan_time() / 2.0;
      const double pq_cost= pq_cpu_cost + pq_io_cost;
      trace_addon.add("priority_queue_cost", pq_cost);

      if (sort_merge_cost < pq_cost)
      {
        trace_addon.add("chosen", false);
        DBUG_RETURN(false);
      }

      trace_addon.add("chosen", true);
      filesort_info->alloc_sort_buffer(param->max_keys_per_buffer,
                                       param->sort_length + param->ref_length);
      if (filesort_info->get_sort_keys())
      {
        // Make attached data to be references instead of fields.
        my_free(filesort_info->addon_buf);
        my_free(filesort_info->addon_field);
        filesort_info->addon_buf= NULL;
        filesort_info->addon_field= NULL;
        param->addon_field= NULL;
        param->addon_length= 0;

        param->res_length= param->ref_length;
        param->sort_length+= param->ref_length;
        param->rec_length= param->sort_length;

        DBUG_RETURN(true);
      }
    }
  }
  DBUG_RETURN(false);
}


int merge_many_buff(Sort_param *param, uchar *sort_buffer,
                    BUFFPEK *buffpek, uint *maxbuffer, IO_CACHE *t_file)
{
  register uint i;
  IO_CACHE t_file2,*from_file,*to_file,*temp;
  BUFFPEK *lastbuff;
  DBUG_ENTER("merge_many_buff");

  if (*maxbuffer < MERGEBUFF2)
    DBUG_RETURN(0);                             /* purecov: inspected */
  if (flush_io_cache(t_file) ||
      open_cached_file(&t_file2,mysql_tmpdir,TEMP_PREFIX,DISK_BUFFER_SIZE,
                        MYF(MY_WME)))
    DBUG_RETURN(1);                             /* purecov: inspected */

  from_file= t_file ; to_file= &t_file2;
  while (*maxbuffer >= MERGEBUFF2)
  {
    if (reinit_io_cache(from_file,READ_CACHE,0L,0,0))
      goto cleanup;
    if (reinit_io_cache(to_file,WRITE_CACHE,0L,0,0))
      goto cleanup;
    lastbuff=buffpek;
    for (i=0 ; i <= *maxbuffer-MERGEBUFF*3/2 ; i+=MERGEBUFF)
    {
      if (merge_buffers(param,from_file,to_file,sort_buffer,lastbuff++,
                        buffpek+i,buffpek+i+MERGEBUFF-1,0))
      goto cleanup;
    }
    if (merge_buffers(param,from_file,to_file,sort_buffer,lastbuff++,
                      buffpek+i,buffpek+ *maxbuffer,0))
      break;                                    /* purecov: inspected */
    if (flush_io_cache(to_file))
      break;                                    /* purecov: inspected */
    temp=from_file; from_file=to_file; to_file=temp;
    setup_io_cache(from_file);
    setup_io_cache(to_file);
    *maxbuffer= (uint) (lastbuff-buffpek)-1;
  }
cleanup:
  close_cached_file(to_file);                   // This holds old result
  if (to_file == t_file)
  {
    *t_file=t_file2;                            // Copy result file
    setup_io_cache(t_file);
  }

  DBUG_RETURN(*maxbuffer >= MERGEBUFF2);        /* Return 1 if interrupted */
} /* merge_many_buff */


uint read_to_buffer(IO_CACHE *fromfile, BUFFPEK *buffpek,
                    uint rec_length)
{
  register uint count;
  uint length;

  if ((count=(uint) min((ha_rows) buffpek->max_keys,buffpek->count)))
  {
    if (mysql_file_pread(fromfile->file, (uchar*) buffpek->base,
                         (length= rec_length*count),
                         buffpek->file_pos, MYF_RW))
      return((uint) -1);                        /* purecov: inspected */
    buffpek->key=buffpek->base;
    buffpek->file_pos+= length;                 /* New filepos */
    buffpek->count-=    count;
    buffpek->mem_count= count;
  }
  return (count*rec_length);
} /* read_to_buffer */


void reuse_freed_buff(QUEUE *queue, BUFFPEK *reuse, uint key_length)
{
  uchar *reuse_end= reuse->base + reuse->max_keys * key_length;
  for (uint i= 0; i < queue->elements; ++i)
  {
    BUFFPEK *bp= (BUFFPEK *) queue_element(queue, i);
    if (bp->base + bp->max_keys * key_length == reuse->base)
    {
      bp->max_keys+= reuse->max_keys;
      return;
    }
    else if (bp->base == reuse_end)
    {
      bp->base= reuse->base;
      bp->max_keys+= reuse->max_keys;
      return;
    }
  }
  DBUG_ASSERT(0);
}


int merge_buffers(Sort_param *param, IO_CACHE *from_file,
                  IO_CACHE *to_file, uchar *sort_buffer,
                  BUFFPEK *lastbuff, BUFFPEK *Fb, BUFFPEK *Tb,
                  int flag)
{
  int error;
  uint rec_length,res_length,offset;
  size_t sort_length;
  ulong maxcount;
  ha_rows max_rows,org_max_rows;
  my_off_t to_start_filepos;
  uchar *strpos;
  BUFFPEK *buffpek;
  QUEUE queue;
  qsort2_cmp cmp;
  void *first_cmp_arg;
  volatile THD::killed_state *killed= &current_thd->killed;
  THD::killed_state not_killable;
  DBUG_ENTER("merge_buffers");

  current_thd->inc_status_sort_merge_passes();
  if (param->not_killable)
  {
    killed= &not_killable;
    not_killable= THD::NOT_KILLED;
  }

  error=0;
  rec_length= param->rec_length;
  res_length= param->res_length;
  sort_length= param->sort_length;
  offset= rec_length-res_length;
  maxcount= (ulong) (param->max_keys_per_buffer / ((uint) (Tb-Fb) +1));
  to_start_filepos= my_b_tell(to_file);
  strpos= (uchar*) sort_buffer;
  org_max_rows=max_rows= param->max_rows;

  /* The following will fire if there is not enough space in sort_buffer */
  DBUG_ASSERT(maxcount!=0);
  
  if (param->unique_buff)
  {
    cmp= param->compare;
    first_cmp_arg= (void *) &param->cmp_context;
  }
  else
  {
    cmp= get_ptr_compare(sort_length);
    first_cmp_arg= (void*) &sort_length;
  }
  if (init_queue(&queue, (uint) (Tb-Fb)+1, offsetof(BUFFPEK,key), 0,
                 (queue_compare) cmp, first_cmp_arg))
    DBUG_RETURN(1);                                /* purecov: inspected */
  for (buffpek= Fb ; buffpek <= Tb ; buffpek++)
  {
    buffpek->base= strpos;
    buffpek->max_keys= maxcount;
    strpos+=
      (uint) (error= (int)read_to_buffer(from_file, buffpek, rec_length));
    if (error == -1)
      goto err;                                 /* purecov: inspected */
    buffpek->max_keys= buffpek->mem_count;      // If less data in buffers than expected
    queue_insert(&queue, (uchar*) buffpek);
  }

  if (param->unique_buff)
  {
    /* 
       Called by Unique::get()
       Copy the first argument to param->unique_buff for unique removal.
       Store it also in 'to_file'.

       This is safe as we know that there is always more than one element
       in each block to merge (This is guaranteed by the Unique:: algorithm
    */
    buffpek= (BUFFPEK*) queue_top(&queue);
    memcpy(param->unique_buff, buffpek->key, rec_length);
    if (my_b_write(to_file, (uchar*) buffpek->key, rec_length))
    {
      error=1; goto err;                        /* purecov: inspected */
    }
    buffpek->key+= rec_length;
    buffpek->mem_count--;
    if (!--max_rows)
    {
      error= 0;                                       /* purecov: inspected */
      goto end;                                       /* purecov: inspected */
    }
    queue_replaced(&queue);                        // Top element has been used
  }
  else
    cmp= 0;                                        // Not unique

  while (queue.elements > 1)
  {
    if (*killed)
    {
      error= 1; goto err;                        /* purecov: inspected */
    }
    for (;;)
    {
      buffpek= (BUFFPEK*) queue_top(&queue);
      if (cmp)                                        // Remove duplicates
      {
        if (!(*cmp)(first_cmp_arg, &(param->unique_buff),
                    (uchar**) &buffpek->key))
              goto skip_duplicate;
            memcpy(param->unique_buff, (uchar*) buffpek->key, rec_length);
      }
      if (flag == 0)
      {
        if (my_b_write(to_file,(uchar*) buffpek->key, rec_length))
        {
          error=1; goto err;                        /* purecov: inspected */
        }
      }
      else
      {
        if (my_b_write(to_file, (uchar*) buffpek->key+offset, res_length))
        {
          error=1; goto err;                        /* purecov: inspected */
        }
      }
      if (!--max_rows)
      {
        error= 0;                               /* purecov: inspected */
        goto end;                               /* purecov: inspected */
      }

    skip_duplicate:
      buffpek->key+= rec_length;
      if (! --buffpek->mem_count)
      {
        if (!(error= (int) read_to_buffer(from_file,buffpek,
                                          rec_length)))
        {
          (void) queue_remove(&queue,0);
          reuse_freed_buff(&queue, buffpek, rec_length);
          break;                        /* One buffer have been removed */
        }
        else if (error == -1)
          goto err;                        /* purecov: inspected */
      }
      queue_replaced(&queue);              /* Top element has been replaced */
    }
  }
  buffpek= (BUFFPEK*) queue_top(&queue);
  buffpek->base= sort_buffer;
  buffpek->max_keys= param->max_keys_per_buffer;

  /*
    As we know all entries in the buffer are unique, we only have to
    check if the first one is the same as the last one we wrote
  */
  if (cmp)
  {
    if (!(*cmp)(first_cmp_arg, &(param->unique_buff), (uchar**) &buffpek->key))
    {
      buffpek->key+= rec_length;         // Remove duplicate
      --buffpek->mem_count;
    }
  }

  do
  {
    if ((ha_rows) buffpek->mem_count > max_rows)
    {                                        /* Don't write too many records */
      buffpek->mem_count= (uint) max_rows;
      buffpek->count= 0;                        /* Don't read more */
    }
    max_rows-= buffpek->mem_count;
    if (flag == 0)
    {
      if (my_b_write(to_file,(uchar*) buffpek->key,
                     (rec_length*buffpek->mem_count)))
      {
        error= 1; goto err;                        /* purecov: inspected */
      }
    }
    else
    {
      register uchar *end;
      strpos= buffpek->key+offset;
      for (end= strpos+buffpek->mem_count*rec_length ;
           strpos != end ;
           strpos+= rec_length)
      {     
        if (my_b_write(to_file, (uchar *) strpos, res_length))
        {
          error=1; goto err;                        
        }
      }
    }
  }
  while ((error=(int) read_to_buffer(from_file,buffpek, rec_length))
         != -1 && error != 0);

end:
  lastbuff->count= min(org_max_rows-max_rows, param->max_rows);
  lastbuff->file_pos= to_start_filepos;
err:
  delete_queue(&queue);
  DBUG_RETURN(error);
} /* merge_buffers */


        /* Do a merge to output-file (save only positions) */

static int merge_index(Sort_param *param, uchar *sort_buffer,
                       BUFFPEK *buffpek, uint maxbuffer,
                       IO_CACHE *tempfile, IO_CACHE *outfile)
{
  DBUG_ENTER("merge_index");
  if (merge_buffers(param,tempfile,outfile,sort_buffer,buffpek,buffpek,
                    buffpek+maxbuffer,1))
    DBUG_RETURN(1);                             /* purecov: inspected */
  DBUG_RETURN(0);
} /* merge_index */


static uint suffix_length(ulong string_length)
{
  if (string_length < 256)
    return 1;
  if (string_length < 256L*256L)
    return 2;
  if (string_length < 256L*256L*256L)
    return 3;
  return 4;                                     // Can't sort longer than 4G
}



uint
sortlength(THD *thd, SORT_FIELD *sortorder, uint s_length,
           bool *multi_byte_charset)
{
  uint total_length= 0;
  const CHARSET_INFO *cs;
  *multi_byte_charset= false;

  for (; s_length-- ; sortorder++)
  {
    sortorder->need_strxnfrm= 0;
    sortorder->suffix_length= 0;
    if (sortorder->field)
    {
      cs= sortorder->field->sort_charset();
      sortorder->length= sortorder->field->sort_length();

      if (use_strnxfrm((cs=sortorder->field->sort_charset())))
      {
        sortorder->need_strxnfrm= 1;
        *multi_byte_charset= 1;
        sortorder->length= cs->coll->strnxfrmlen(cs, sortorder->length);
      }
      if (sortorder->field->maybe_null())
        total_length++;                       // Place for NULL marker

      if (sortorder->field->result_type() == STRING_RESULT &&
          !sortorder->field->is_temporal())
      {
        set_if_smaller(sortorder->length, thd->variables.max_sort_length);
      }
    }
    else
    {
      sortorder->result_type= sortorder->item->result_type();
      if (sortorder->item->is_temporal())
        sortorder->result_type= INT_RESULT;
      switch (sortorder->result_type) {
      case STRING_RESULT:
        sortorder->length= sortorder->item->max_length;
        set_if_smaller(sortorder->length, thd->variables.max_sort_length);
        if (use_strnxfrm((cs=sortorder->item->collation.collation)))
        { 
          sortorder->length= cs->coll->strnxfrmlen(cs, sortorder->length);
          sortorder->need_strxnfrm= 1;
          *multi_byte_charset= 1;
        }
        else if (cs == &my_charset_bin)
        {
          /* Store length last to be able to sort blob/varbinary */
          sortorder->suffix_length= suffix_length(sortorder->length);
          sortorder->length+= sortorder->suffix_length;
        }
        break;
      case INT_RESULT:
#if SIZEOF_LONG_LONG > 4
        sortorder->length=8;                    // Size of intern longlong
#else
        sortorder->length=4;
#endif
        break;
      case DECIMAL_RESULT:
        sortorder->length=
          my_decimal_get_binary_size(sortorder->item->max_length - 
                                     (sortorder->item->decimals ? 1 : 0),
                                     sortorder->item->decimals);
        break;
      case REAL_RESULT:
        sortorder->length=sizeof(double);
        break;
      case ROW_RESULT:
      default: 
        // This case should never be choosen
        DBUG_ASSERT(0);
        break;
      }
      if (sortorder->item->maybe_null)
        total_length++;                       // Place for NULL marker
    }
    total_length+= sortorder->length;
  }
  sortorder->field= NULL;                       // end marker
  DBUG_PRINT("info",("sort_length: %u", total_length));
  return total_length;
}


static SORT_ADDON_FIELD *
get_addon_fields(ulong max_length_for_sort_data,
                 Field **ptabfield, uint sortlength, uint *plength)
{
  Field **pfield;
  Field *field;
  SORT_ADDON_FIELD *addonf;
  uint length= 0;
  uint fields= 0;
  uint null_fields= 0;
  MY_BITMAP *read_set= (*ptabfield)->table->read_set;

  /*
    If there is a reference to a field in the query add it
    to the the set of appended fields.
    Note for future refinement:
    This this a too strong condition.
    Actually we need only the fields referred in the
    result set. And for some of them it makes sense to use 
    the values directly from sorted fields.
  */
  *plength= 0;

  for (pfield= ptabfield; (field= *pfield) ; pfield++)
  {
    if (!bitmap_is_set(read_set, field->field_index))
      continue;
    if (field->flags & BLOB_FLAG)
      return 0;
    length+= field->max_packed_col_length(field->pack_length());
    if (field->maybe_null())
      null_fields++;
    fields++;
  } 
  if (!fields)
    return 0;
  length+= (null_fields+7)/8;

  if (length+sortlength > max_length_for_sort_data ||
      !(addonf= (SORT_ADDON_FIELD *) my_malloc(sizeof(SORT_ADDON_FIELD)*
                                               (fields+1), MYF(MY_WME))))
    return 0;

  *plength= length;
  length= (null_fields+7)/8;
  null_fields= 0;
  for (pfield= ptabfield; (field= *pfield) ; pfield++)
  {
    if (!bitmap_is_set(read_set, field->field_index))
      continue;
    addonf->field= field;
    addonf->offset= length;
    if (field->maybe_null())
    {
      addonf->null_offset= null_fields/8;
      addonf->null_bit= 1<<(null_fields & 7);
      null_fields++;
    }
    else
    {
      addonf->null_offset= 0;
      addonf->null_bit= 0;
    }
    addonf->length= field->max_packed_col_length(field->pack_length());
    length+= addonf->length;
    addonf++;
  }
  addonf->field= 0;     // Put end marker
  
  DBUG_PRINT("info",("addon_length: %d",length));
  return (addonf-fields);
}


static void 
unpack_addon_fields(struct st_sort_addon_field *addon_field, uchar *buff)
{
  Field *field;
  SORT_ADDON_FIELD *addonf= addon_field;

  for ( ; (field= addonf->field) ; addonf++)
  {
    if (addonf->null_bit && (addonf->null_bit & buff[addonf->null_offset]))
    {
      field->set_null();
      continue;
    }
    field->set_notnull();
    field->unpack(field->ptr, buff + addonf->offset);
  }
}

/*
** functions to change a double or float to a sortable string
** The following should work for IEEE
*/

#define DBL_EXP_DIG (sizeof(double)*8-DBL_MANT_DIG)

void change_double_for_sort(double nr,uchar *to)
{
  uchar *tmp=(uchar*) to;
  if (nr == 0.0)
  {                                             /* Change to zero string */
    tmp[0]=(uchar) 128;
    memset(tmp+1, 0, sizeof(nr)-1);
  }
  else
  {
#ifdef WORDS_BIGENDIAN
    memcpy(tmp, &nr, sizeof(nr));
#else
    {
      uchar *ptr= (uchar*) &nr;
#if defined(__FLOAT_WORD_ORDER) && (__FLOAT_WORD_ORDER == __BIG_ENDIAN)
      tmp[0]= ptr[3]; tmp[1]=ptr[2]; tmp[2]= ptr[1]; tmp[3]=ptr[0];
      tmp[4]= ptr[7]; tmp[5]=ptr[6]; tmp[6]= ptr[5]; tmp[7]=ptr[4];
#else
      tmp[0]= ptr[7]; tmp[1]=ptr[6]; tmp[2]= ptr[5]; tmp[3]=ptr[4];
      tmp[4]= ptr[3]; tmp[5]=ptr[2]; tmp[6]= ptr[1]; tmp[7]=ptr[0];
#endif
    }
#endif
    if (tmp[0] & 128)                           /* Negative */
    {                                           /* make complement */
      uint i;
      for (i=0 ; i < sizeof(nr); i++)
        tmp[i]=tmp[i] ^ (uchar) 255;
    }
    else
    {                                   /* Set high and move exponent one up */
      ushort exp_part=(((ushort) tmp[0] << 8) | (ushort) tmp[1] |
                       (ushort) 32768);
      exp_part+= (ushort) 1 << (16-1-DBL_EXP_DIG);
      tmp[0]= (uchar) (exp_part >> 8);
      tmp[1]= (uchar) exp_part;
    }
  }
}