/* Copyright (c) 2000, 2015, Oracle and/or its affiliates.
   Copyright (c) 2009, 2015, MariaDB

   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 Street, Fifth Floor, Boston, MA  02110-1301, USA */


/**
  @file

  @brief
  Sorts a database
*/

#include <my_global.h>
#include "sql_priv.h"
#include "filesort.h"
#ifdef HAVE_STDDEF_H
#include <stddef.h>			/* for macro offsetof */
#endif
#include <m_ctype.h>
#include "sql_sort.h"
#include "probes_mysql.h"
#include "sql_base.h"
#include "sql_test.h"                           // TEST_filesort
#include "opt_range.h"                          // SQL_SELECT
#include "bounded_queue.h"
#include "filesort_utils.h"
#include "sql_select.h"
#include "log_slow.h"
#include "debug_sync.h"

/// How to write record_ref.
#define WRITE_REF(file,from) \
if (my_b_write((file),(uchar*) (from),param->ref_length)) \
  DBUG_RETURN(1);

	/* 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(THD *thd, Sort_param *param, SQL_SELECT *select,
                             SORT_INFO *fs_info,
                             IO_CACHE *buffer_file,
                             IO_CACHE *tempfile,
                             Bounded_queue<uchar, uchar> *pq,
                             ha_rows *found_rows);
static bool write_keys(Sort_param *param, SORT_INFO *fs_info,
                      uint count, IO_CACHE *buffer_file, IO_CACHE *tempfile);
static void make_sortkey(Sort_param *param, uchar *to, uchar *ref_pos);
static void register_used_fields(Sort_param *param);
static bool save_index(Sort_param *param, uint count,
                       SORT_INFO *table_sort);
static uint suffix_length(ulong string_length);
static uint sortlength(THD *thd, SORT_FIELD *sortorder, uint s_length,
		       bool *multi_byte_charset);
static SORT_ADDON_FIELD *get_addon_fields(ulong max_length_for_sort_data,
                                          Field **ptabfield,
                                          uint sortlength,
                                          LEX_STRING *addon_buf);
static void unpack_addon_fields(struct st_sort_addon_field *addon_field,
                                uchar *buff, uchar *buff_end);
static bool check_if_pq_applicable(Sort_param *param, SORT_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)
{
  DBUG_ASSERT(addon_field == 0 && addon_buf.length == 0);

  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_buf.length
    */
    addon_field= get_addon_fields(max_length_for_sort_data,
                                  table->field, sort_length, &addon_buf);
  }
  if (addon_field)
    res_length= addon_buf.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_buf.length;
  max_rows= maxrows;
}


/**
  Sort a table.
  Creates a set of pointers that can be used to read the rows
  in sorted order. This should be done with the functions
  in records.cc.

  Before calling filesort, one must have done
  table->file->info(HA_STATUS_VARIABLE)

  The result set is stored in
  filesort_info->io_cache or
  filesort_info->record_pointers.

  @param      thd            Current thread
  @param      table          Table to sort
  @param      filesort       How to sort the table
  @param[out] found_rows     Store the number of found rows here.
                             This is the number of found rows after
                             applying WHERE condition.
  @note
    If we sort by position (like if filesort->sort_positions==true) 
    filesort() will call table->prepare_for_position().

  @retval
    0			Error
    #			SORT_INFO
*/

SORT_INFO *filesort(THD *thd, TABLE *table, Filesort *filesort,
                    Filesort_tracker* tracker, JOIN *join,
                    table_map first_table_bit)
{
  int error;
  DBUG_ASSERT(thd->variables.sortbuff_size <= SIZE_T_MAX);
  size_t memory_available= (size_t)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;
  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(thd, join, first_table_bit)))
    DBUG_RETURN(NULL);  /* purecov: inspected */

  DBUG_EXECUTE("info",TEST_filesort(filesort->sortorder,s_length););
#ifdef SKIP_DBUG_IN_FILESORT
  DBUG_PUSH("");		/* No DBUG here */
#endif
  SORT_INFO *sort;
  TABLE_LIST *tab= table->pos_in_table_list;
  Item_subselect *subselect= tab ? tab->containing_subselect() : 0;
  MYSQL_FILESORT_START(table->s->db.str, table->s->table_name.str);
  DEBUG_SYNC(thd, "filesort_start");

  if (!(sort= new SORT_INFO))
    return 0;

  if (subselect && subselect->filesort_buffer.is_allocated())
  {
    /* Reuse cache from last call */
    sort->filesort_buffer= subselect->filesort_buffer;
    sort->buffpek= subselect->sortbuffer;
    subselect->filesort_buffer.reset();
    subselect->sortbuffer.str=0;
  }

  outfile= &sort->io_cache;

  my_b_clear(&tempfile);
  my_b_clear(&buffpek_pointers);
  buffpek=0;
  error= 1;
  sort->found_rows= HA_POS_ERROR;

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

  sort->addon_buf=    param.addon_buf;
  sort->addon_field=  param.addon_field;
  sort->unpack=       unpack_addon_fields;
  if (multi_byte_charset &&
      !(param.tmp_buffer= (char*) my_malloc(param.sort_length,
                                            MYF(MY_WME | MY_THREAD_SPECIFIC))))
    goto err;

  if (select && select->quick)
    thd->inc_status_sort_range();
  else
    thd->inc_status_sort_scan();
  thd->query_plan_flags|= QPLAN_FILESORT;
  tracker->report_use(max_rows);

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

  if (check_if_pq_applicable(&param, sort,
                             table, num_rows, memory_available))
  {
    DBUG_PRINT("info", ("filesort PQ is applicable"));
    thd->query_plan_flags|= QPLAN_FILESORT_PRIORITY_QUEUE;
    status_var_increment(thd->status_var.filesort_pq_sorts_);
    tracker->incr_pq_used();
    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, 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"));
      DBUG_ASSERT(thd->is_error());
      goto err;
    }
    // For PQ queries (with limit) we initialize all pointers.
    sort->init_record_pointers();
  }
  else
  {
    DBUG_PRINT("info", ("filesort PQ is not applicable"));

    size_t min_sort_memory= MY_MAX(MIN_SORT_MEMORY,
                                   param.sort_length*MERGEBUFF2);
    set_if_bigger(min_sort_memory, sizeof(BUFFPEK*)*MERGEBUFF2);
    while (memory_available >= min_sort_memory)
    {
      ulonglong keys= memory_available / (param.rec_length + sizeof(char*));
      param.max_keys_per_buffer= (uint) MY_MIN(num_rows, keys);
      if (sort->alloc_sort_buffer(param.max_keys_per_buffer, param.rec_length))
        break;
      size_t 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;
    }
    tracker->report_sort_buffer_size(sort->sort_buffer_size());
  }

  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;
  num_rows= find_all_keys(thd, &param, select,
                          sort,
                          &buffpek_pointers,
                          &tempfile, 
                          pq.is_initialized() ? &pq : NULL,
                          &sort->found_rows);
  if (num_rows == HA_POS_ERROR)
    goto err;

  maxbuffer= (uint) (my_b_tell(&buffpek_pointers)/sizeof(*buffpek));
  tracker->report_merge_passes_at_start(thd->query_plan_fsort_passes);
  tracker->report_row_numbers(param.examined_rows, sort->found_rows, num_rows);

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

    if (sort->buffpek.str && sort->buffpek.length < maxbuffer)
    {
      my_free(sort->buffpek.str);
      sort->buffpek.str= 0;
    }
    if (!(sort->buffpek.str=
          (char *) read_buffpek_from_file(&buffpek_pointers, maxbuffer,
                                          (uchar*) sort->buffpek.str)))
      goto err;
    sort->buffpek.length= maxbuffer;
    buffpek= (BUFFPEK *) sort->buffpek.str;
    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=((param.max_keys_per_buffer *
                                (param.rec_length + sizeof(char*))) /
                               param.rec_length - 1);
    maxbuffer--;				// Offset from 0
    if (merge_many_buff(&param,
                        (uchar*) 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*) 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())
  {
    sort->free_sort_buffer();
    my_free(sort->buffpek.str);
  }
  else
  {
    /* Remember sort buffers for next subquery call */
    subselect->filesort_buffer= sort->filesort_buffer;
    subselect->sortbuffer=      sort->buffpek;
    sort->filesort_buffer.reset();              // Don't free this
  }
  sort->buffpek.str= 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;
    }
  }
  tracker->report_merge_passes_at_end(thd->query_plan_fsort_passes);
  if (error)
  {
    int kill_errno= thd->killed_errno();
    DBUG_ASSERT(thd->is_error() || kill_errno || thd->killed == ABORT_QUERY);

    my_printf_error(ER_FILSORT_ABORT,
                    "%s: %s",
                    MYF(0),
                    ER_THD(thd, ER_FILSORT_ABORT),
                    kill_errno ? ER_THD(thd, kill_errno) :
                    thd->killed == ABORT_QUERY ? "" :
                    thd->get_stmt_da()->message());

    if (global_system_variables.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);

  sort->examined_rows= param.examined_rows;
  sort->return_rows= num_rows;
#ifdef SKIP_DBUG_IN_FILESORT
  DBUG_POP();			/* Ok to DBUG */
#endif

  DBUG_PRINT("exit",
             ("num_rows: %lld examined_rows: %lld found_rows: %lld",
              (longlong) sort->return_rows, (longlong) sort->examined_rows,
              (longlong) sort->found_rows));
  MYSQL_FILESORT_DONE(error, num_rows);

  if (error)
  {
    delete sort;
    sort= 0;
  }
  DBUG_RETURN(sort);
} /* filesort */


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


uint Filesort::make_sortorder(THD *thd, JOIN *join, table_map first_table_bit)
{
  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*) thd->alloc(sizeof(SORT_FIELD) * (count + 1));
  pos= sort= sortorder;

  if (!pos)
    DBUG_RETURN(0);

  for (ord= order; ord; ord= ord->next, pos++)
  {
    Item *first= ord->item[0];
    /*
      It is possible that the query plan is to read table t1, while the
      sort criteria actually has "ORDER BY t2.col" and the WHERE clause has
      a multi-equality(t1.col, t2.col, ...).
      The optimizer detects such cases (grep for
      UseMultipleEqualitiesToRemoveTempTable to see where), but doesn't
      perform equality substitution in the order->item. We need to do the
      substitution here ourselves.
    */
    table_map item_map= first->used_tables();
    if (join && (item_map & ~join->const_table_map) &&
        !(item_map & first_table_bit) && join->cond_equal &&
         first->get_item_equal())
    {
      /*
        Ok, this is the case descibed just above. Get the first element of the
        multi-equality.
      */
      Item_equal *item_eq= first->get_item_equal();
      first= item_eq->get_first(NO_PARTICULAR_TAB, NULL);
    }

    Item *item= first->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);
}


/** Read 'count' number of buffer pointers into memory. */

static uchar *read_buffpek_from_file(IO_CACHE *buffpek_pointers, uint count,
                                     uchar *buf)
{
  size_t 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 | MY_THREAD_SPECIFIC));
  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

/* Buffer where record is returned */
char dbug_print_row_buff[512];

/* Temporary buffer for printing a column */
char dbug_print_row_buff_tmp[512];

/*
  Print table's current row into a buffer and return a pointer to it.

  This is intended to be used from gdb:
  
    (gdb) p dbug_print_table_row(table)
      $33 = "SUBQUERY2_t1(col_int_key,col_varchar_nokey)=(7,c)"
    (gdb)

  Only columns in table->read_set are printed
*/

const char* dbug_print_table_row(TABLE *table)
{
  Field **pfield;
  String tmp(dbug_print_row_buff_tmp,
             sizeof(dbug_print_row_buff_tmp),&my_charset_bin);

  String output(dbug_print_row_buff, sizeof(dbug_print_row_buff),
                &my_charset_bin);

  output.length(0);
  output.append(table->alias);
  output.append("(");
  bool first= true;

  for (pfield= table->field; *pfield ; pfield++)
  {
    if (table->read_set && !bitmap_is_set(table->read_set, (*pfield)->field_index))
      continue;
    
    if (first)
      first= false;
    else
      output.append(",");

    output.append((*pfield)->field_name? (*pfield)->field_name: "NULL");
  }

  output.append(")=(");

  first= true;
  for (pfield= table->field; *pfield ; pfield++)
  {
    Field *field=  *pfield;

    if (table->read_set && !bitmap_is_set(table->read_set, (*pfield)->field_index))
      continue;

    if (first)
      first= false;
    else
      output.append(",");

    if (field->is_null())
      output.append("NULL");
    else
    {
      if (field->type() == MYSQL_TYPE_BIT)
        (void) field->val_int_as_str(&tmp, 1);
      else
        field->val_str(&tmp);
      output.append(tmp.ptr(), tmp.length());
    }
  }
  output.append(")");
  
  return output.c_ptr_safe();
}


/*
  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 


/**
  Search after sort_keys, and write them into tempfile
  (if we run out of space in the sort_keys buffer).
  All produced sequences are guaranteed to be non-empty.

  @param param             Sorting parameter
  @param select            Use this to get source data
  @param sort_keys         Array of pointers to sort key + addon buffers.
  @param buffpek_pointers  File to write BUFFPEKs describing sorted segments
                           in tempfile.
  @param tempfile          File to write sorted sequences of sortkeys to.
  @param pq                If !NULL, use it for keeping top N elements
  @param [out] found_rows  The number of FOUND_ROWS().
                           For a query with LIMIT, this value will typically
                           be larger than the function return value.

  @note
    Basic idea:
    @verbatim
     while (get_next_sortkey())
     {
       if (using priority queue)
         push sort key into queue
       else
       {
         if (no free space in sort_keys buffers)
         {
           sort sort_keys buffer;
           dump sorted sequence to 'tempfile';
           dump BUFFPEK describing sequence location into 'buffpek_pointers';
         }
         put sort key into 'sort_keys';
       }
     }
     if (sort_keys has some elements && dumped at least once)
       sort-dump-dump as above;
     else
       don't sort, leave sort_keys array to be sorted by caller.
  @endverbatim

  @retval
    Number of records written on success.
  @retval
    HA_POS_ERROR on error.
*/

static ha_rows find_all_keys(THD *thd, Sort_param *param, SQL_SELECT *select,
                             SORT_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;
  handler *file;
  MY_BITMAP *save_read_set, *save_write_set, *save_vcol_set;
  Item *sort_cond;
  ha_rows retval;
  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;

  DBUG_EXECUTE_IF("show_explain_in_find_all_keys", 
                  dbug_serve_apcs(thd, 1);
                 );

  if (!quick_select)
  {
    next_pos=(uchar*) 0;			/* Find records in sequence */
    DBUG_EXECUTE_IF("bug14365043_1",
                    DBUG_SET("+d,ha_rnd_init_fail"););
    if (file->ha_rnd_init_with_error(1))
      DBUG_RETURN(HA_POS_ERROR);
    file->extra_opt(HA_EXTRA_CACHE, thd->variables.read_buff_size);
  }

  /* Remember original bitmaps */
  save_read_set=  sort_form->read_set;
  save_write_set= sort_form->write_set;
  save_vcol_set=  sort_form->vcol_set;

  /* Set up temporary column read map for columns used by sort */
  DBUG_ASSERT(save_read_set != &sort_form->tmp_set);
  bitmap_clear_all(&sort_form->tmp_set);
  sort_form->column_bitmaps_set(&sort_form->tmp_set, &sort_form->tmp_set, 
                                &sort_form->tmp_set);
  register_used_fields(param);
  if (quick_select)
    select->quick->add_used_key_part_to_set();

  sort_cond= (!select ? 0 :
              (!select->pre_idx_push_select_cond ?
               select->cond : select->pre_idx_push_select_cond));
  if (sort_cond)
    sort_cond->walk(&Item::register_field_in_read_map, 1, sort_form);
  sort_form->file->column_bitmaps_signal();

  if (quick_select)
  {
    if (select->quick->reset())
      goto err;
  }

  DEBUG_SYNC(thd, "after_index_merge_phase1");
  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 (thd->check_killed())
    {
      DBUG_PRINT("info",("Sort killed by user"));
      if (!quick_select)
      {
        (void) file->extra(HA_EXTRA_NO_CACHE);
        file->ha_rnd_end();
      }
      goto err;                               /* purecov: inspected */
    }

    bool write_record= false;
    if (error == 0)
    {
      param->examined_rows++;
      if (select && select->cond)
      {
        /*
          If the condition 'select->cond' contains a subquery, restore the
          original read/write sets of the table 'sort_form' because when
          SQL_SELECT::skip_record evaluates this condition. it may include a
          correlated subquery predicate, such that some field in the subquery
          refers to 'sort_form'.

          PSergey-todo: discuss the above with Timour.
        */
        MY_BITMAP *tmp_read_set= sort_form->read_set;
        MY_BITMAP *tmp_write_set= sort_form->write_set;
        MY_BITMAP *tmp_vcol_set= sort_form->vcol_set;

        if (select->cond->with_subselect)
          sort_form->column_bitmaps_set(save_read_set, save_write_set,
                                        save_vcol_set);
        write_record= (select->skip_record(thd) > 0);
        if (select->cond->with_subselect)
          sort_form->column_bitmaps_set(tmp_read_set,
                                        tmp_write_set,
                                        tmp_vcol_set);
      }
      else
        write_record= true;
    }

    if (write_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))
            goto err;
	  idx= 0;
	  indexpos++;
        }
        make_sortkey(param, fs_info->get_record_buffer(idx++), ref_pos);
      }
    }

    /* It does not make sense to read more keys in case of a fatal error */
    if (thd->is_error())
      break;

    /*
      We need to this after checking the error as the transaction may have
      rolled back in case of a deadlock
    */
    if (!write_record)
      file->unlock_row();
  }
  if (!quick_select)
  {
    (void) file->extra(HA_EXTRA_NO_CACHE);	/* End cacheing of records */
    if (!next_pos)
      file->ha_rnd_end();
  }

  /* Signal we should use orignal column read and write maps */
  sort_form->column_bitmaps_set(save_read_set, save_write_set, save_vcol_set);

  if (thd->is_error())
    DBUG_RETURN(HA_POS_ERROR);

  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 */
  retval= (my_b_inited(tempfile) ?
           (ha_rows) (my_b_tell(tempfile)/param->rec_length) :
           idx);
  DBUG_PRINT("info", ("find_all_keys return %llu", (ulonglong) retval));
  DBUG_RETURN(retval);

err:
  sort_form->column_bitmaps_set(save_read_set, save_write_set, save_vcol_set);
  DBUG_RETURN(HA_POS_ERROR);
} /* find_all_keys */


/**
  @details
  Sort the buffer and write:
  -# the sorted sequence to tempfile
  -# a BUFFPEK describing the sorted sequence position to buffpek_pointers

    (was: Skriver en buffert med nycklar till filen)

  @param param             Sort parameters
  @param sort_keys         Array of pointers to keys to sort
  @param count             Number of elements in sort_keys array
  @param buffpek_pointers  One 'BUFFPEK' struct will be written into this file.
                           The BUFFPEK::{file_pos, count} will indicate where
                           the sorted data was stored.
  @param tempfile          The sorted sequence will be written into this file.

  @retval
    0 OK
  @retval
    1 Error
*/

static bool
write_keys(Sort_param *param,  SORT_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;
  bzero(&buffpek, sizeof(buffpek));
  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 */


/**
  Store length as suffix in high-byte-first order.
*/

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;
  }
}


void
Type_handler_string_result::make_sort_key(uchar *to, Item *item,
                                          const SORT_FIELD_ATTR *sort_field,
                                          Sort_param *param) const
{
  CHARSET_INFO *cs= item->collation.collation;
  bool maybe_null= item->maybe_null;

  if (maybe_null)
    *to++= 1;
  char *tmp_buffer= param->tmp_buffer ? param->tmp_buffer : (char*) to;
  String tmp(tmp_buffer, param->tmp_buffer ? param->sort_length :
                                             sort_field->length, 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 */
    }
    return;
  }

  if (use_strnxfrm(cs))
  {
    uint tmp_length __attribute__((unused));
    tmp_length= cs->coll->strnxfrm(cs, to, sort_field->length,
                                   item->max_char_length() *
                                   cs->strxfrm_multiply,
                                   (uchar*) res->ptr(), res->length(),
                                   MY_STRXFRM_PAD_WITH_SPACE |
                                   MY_STRXFRM_PAD_TO_MAXLEN);
    DBUG_ASSERT(tmp_length == sort_field->length);
  }
  else
  {
    uint diff;
    uint sort_field_length= sort_field->length - sort_field->suffix_length;
    uint length= res->length();
    if (sort_field_length < length)
    {
      diff= 0;
      length= sort_field_length;
    }
    else
      diff= sort_field_length - length;
    if (sort_field->suffix_length)
    {
      /* Store length last in result_string */
      store_length(to + sort_field_length, length, sort_field->suffix_length);
    }
    /* apply cs->sort_order for case-insensitive comparison if needed */
    my_strnxfrm(cs,(uchar*)to,length,(const uchar*)res->ptr(),length);
    char fill_char= ((cs->state & MY_CS_BINSORT) ? (char) 0 : ' ');
    cs->cset->fill(cs, (char *)to+length,diff,fill_char);
  }
}


void
Type_handler_int_result::make_sort_key(uchar *to, Item *item,
                                       const SORT_FIELD_ATTR *sort_field,
                                       Sort_param *param) const
{
  longlong value= item->val_int_result();
  make_sort_key_longlong(to, item->maybe_null, item->null_value,
                         item->unsigned_flag, value);
}


void
Type_handler_temporal_result::make_sort_key(uchar *to, Item *item,
                                            const SORT_FIELD_ATTR *sort_field,
                                            Sort_param *param) const
{
  MYSQL_TIME buf;
  if (item->get_date_result(&buf, TIME_INVALID_DATES))
  {
    DBUG_ASSERT(item->maybe_null);
    DBUG_ASSERT(item->null_value);
    make_sort_key_longlong(to, item->maybe_null, true,
                           item->unsigned_flag, 0);
  }
  else
    make_sort_key_longlong(to, item->maybe_null, false,
                           item->unsigned_flag, pack_time(&buf));
}


void
Type_handler::make_sort_key_longlong(uchar *to,
                                     bool maybe_null,
                                     bool null_value,
                                     bool unsigned_flag,
                                     longlong value) const

{
  if (maybe_null)
  {
    if (null_value)
    {
      memset(to, 0, 9);
      return;
    }
    *to++= 1;
  }
  to[7]= (uchar) value;
  to[6]= (uchar) (value >> 8);
  to[5]= (uchar) (value >> 16);
  to[4]= (uchar) (value >> 24);
  to[3]= (uchar) (value >> 32);
  to[2]= (uchar) (value >> 40);
  to[1]= (uchar) (value >> 48);
  if (unsigned_flag)                    /* Fix sign */
    to[0]= (uchar) (value >> 56);
  else
    to[0]= (uchar) (value >> 56) ^ 128;	/* Reverse signbit */
}


void
Type_handler_decimal_result::make_sort_key(uchar *to, Item *item,
                                           const SORT_FIELD_ATTR *sort_field,
                                           Sort_param *param) const
{
  my_decimal dec_buf, *dec_val= item->val_decimal_result(&dec_buf);
  if (item->maybe_null)
  {
    if (item->null_value)
    {
      memset(to, 0, sort_field->length + 1);
      return;
    }
    *to++= 1;
  }
  my_decimal2binary(E_DEC_FATAL_ERROR, dec_val, to,
                    item->max_length - (item->decimals ? 1 : 0),
                    item->decimals);
}


void
Type_handler_real_result::make_sort_key(uchar *to, Item *item,
                                        const SORT_FIELD_ATTR *sort_field,
                                        Sort_param *param) const
{
  double value= item->val_result();
  if (item->maybe_null)
  {
    if (item->null_value)
    {
      memset(to, 0, sort_field->length + 1);
      return;
    }
    *to++= 1;
  }
  change_double_for_sort(value, to);
}


/** Make a sort-key from record. */

static void make_sortkey(register Sort_param *param,
                         register uchar *to, uchar *ref_pos)
{
  reg3 Field *field;
  reg1 SORT_FIELD *sort_field;
  reg5 uint length;

  for (sort_field=param->local_sortorder ;
       sort_field != param->end ;
       sort_field++)
  {
    bool maybe_null=0;
    if ((field=sort_field->field))
    {						// Field
      field->make_sort_key(to, sort_field->length);
      if ((maybe_null = field->maybe_null()))
        to++;
    }
    else
    {						// Item
      sort_field->item->make_sort_key(to, sort_field->item, sort_field, param);
      if ((maybe_null= sort_field->item->maybe_null))
        to++;
    }
    if (sort_field->reverse)
    {							/* Revers key */
      if (maybe_null && (to[-1]= !to[-1]))
      {
        to+= sort_field->length; // don't waste the time reversing all 0's
        continue;
      }
      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= addonf->field) ; addonf++)
    {
      if (addonf->null_bit && field->is_null())
      {
        nulls[addonf->null_offset]|= addonf->null_bit;
#ifdef HAVE_valgrind
	bzero(to, addonf->length);
#endif
      }
      else
      {
#ifdef HAVE_valgrind
        uchar *end= field->pack(to, field->ptr);
	uint length= (uint) ((to + addonf->length) - end);
	DBUG_ASSERT((int) length >= 0);
	if (length)
	  bzero(end, length);
#else
        (void) field->pack(to, field->ptr);
#endif
      }
      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;

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

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


static bool save_index(Sort_param *param, uint count,
                       SORT_INFO *table_sort)
{
  uint offset,res_length;
  uchar *to;
  DBUG_ENTER("save_index");
  DBUG_ASSERT(table_sort->record_pointers == 0);

  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 | MY_THREAD_SPECIFIC))))
    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);
}


/**
  Test whether priority queue is worth using to get top elements of an
  ordered result set. If it is, then allocates buffer for required amount of
  records

  @param param            Sort parameters.
  @param filesort_info    Filesort information.
  @param table            Table to sort.
  @param num_rows         Estimate of number of rows in source record set.
  @param memory_available Memory available for sorting.

  DESCRIPTION
    Given a query like this:
      SELECT ... FROM t ORDER BY a1,...,an LIMIT max_rows;
    This function tests whether a priority queue should be used to keep
    the result. Necessary conditions are:
    - estimate that it is actually cheaper than merge-sort
    - enough memory to store the <max_rows> records.

    If we don't have space for <max_rows> records, but we *do* have
    space for <max_rows> keys, we may rewrite 'table' to sort with
    references to records instead of additional data.
    (again, based on estimates that it will actually be cheaper).

   @retval
    true  - if it's ok to use PQ
    false - PQ will be slower than merge-sort, or there is not enough memory.
*/

bool check_if_pq_applicable(Sort_param *param,
                            SORT_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;

  if (param->max_rows == HA_POS_ERROR)
  {
    DBUG_PRINT("info", ("No LIMIT"));
    DBUG_RETURN(false);
  }

  if (param->max_rows + 2 >= UINT_MAX)
  {
    DBUG_PRINT("info", ("Too large LIMIT"));
    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 )
    {
      DBUG_RETURN(filesort_info->alloc_sort_buffer(param->max_keys_per_buffer,
                                                   param->rec_length) != NULL);
    }
    else
    {
      // PQ will be slower.
      DBUG_RETURN(false);
    }
  }

  // Do we have space for LIMIT rows in memory?
  if (param->max_keys_per_buffer < num_available_keys)
  {
    DBUG_RETURN(filesort_info->alloc_sort_buffer(param->max_keys_per_buffer,
                                                 param->rec_length) != 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;

    // Can we fit all the keys in memory?
    if (param->max_keys_per_buffer < num_available_keys)
    {
      const double sort_merge_cost=
        get_merge_many_buffs_cost_fast(num_rows,
                                       num_available_keys,
                                       row_length);
      /*
        PQ has cost:
        (insert + qsort) * log(queue size) / TIME_FOR_COMPARE_ROWID +
        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) / TIME_FOR_COMPARE_ROWID;
      const double pq_io_cost=
        param->max_rows * table->file->scan_time() / 2.0;
      const double pq_cost= pq_cpu_cost + pq_io_cost;

      if (sort_merge_cost < pq_cost)
        DBUG_RETURN(false);

      if (filesort_info->alloc_sort_buffer(param->max_keys_per_buffer,
                                           param->sort_length +
                                           param->ref_length))
      {
        /* Make attached data to be references instead of fields. */
        my_free(filesort_info->addon_field);
        filesort_info->addon_field= NULL;
        param->addon_field= NULL;

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

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


/** Merge buffers to make < MERGEBUFF2 buffers. */

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;
    *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
  }

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


/**
  Read data to buffer.

  @retval
    (uint)-1 if something goes wrong
*/

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

  if ((count=(uint) MY_MIN((ha_rows) buffpek->max_keys,buffpek->count)))
  {
    if (my_b_pread(fromfile, (uchar*) buffpek->base,
                   (length= rec_length*count), buffpek->file_pos))
      return ((uint) -1);
    buffpek->key=buffpek->base;
    buffpek->file_pos+= length;			/* New filepos */
    buffpek->count-=	count;
    buffpek->mem_count= count;
  }
  return (count*rec_length);
} /* read_to_buffer */


/**
  Put all room used by freed buffer to use in adjacent buffer.

  Note, that we can't simply distribute memory evenly between all buffers,
  because new areas must not overlap with old ones.

  @param[in] queue      list of non-empty buffers, without freed buffer
  @param[in] reuse      empty buffer
  @param[in] key_length key length
*/

void reuse_freed_buff(QUEUE *queue, BUFFPEK *reuse, uint key_length)
{
  uchar *reuse_end= reuse->base + reuse->max_keys * key_length;
  for (uint i= queue_first_element(queue);
       i <= queue_last_element(queue);
       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);
}


/**
  Merge buffers to one buffer.

  @param param        Sort parameter
  @param from_file    File with source data (BUFFPEKs point to this file)
  @param to_file      File to write the sorted result data.
  @param sort_buffer  Buffer for data to store up to MERGEBUFF2 sort keys.
  @param lastbuff     OUT Store here BUFFPEK describing data written to to_file
  @param Fb           First element in source BUFFPEKs array
  @param Tb           Last element in source BUFFPEKs array
  @param flag

  @retval
    0      OK
  @retval
    other  error
*/

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;
  element_count dupl_count= 0;
  uchar *src;
  uchar *unique_buff= param->unique_buff;
  const bool killable= !param->not_killable;
  THD* const thd=current_thd;
  DBUG_ENTER("merge_buffers");

  thd->inc_status_sort_merge_passes();
  thd->query_plan_fsort_passes++;

  error=0;
  rec_length= param->rec_length;
  res_length= param->res_length;
  sort_length= param->sort_length;
  uint dupl_count_ofs= rec_length-sizeof(element_count);
  uint min_dupl_count= param->min_dupl_count;
  bool check_dupl_count= flag && min_dupl_count;
  offset= (rec_length-
           (flag && min_dupl_count ? sizeof(dupl_count) : 0)-res_length);
  uint wr_len= flag ? res_length : rec_length;
  uint wr_offset= flag ? offset : 0;
  maxcount= (ulong) (param->max_keys_per_buffer/((uint) (Tb-Fb) +1));
  to_start_filepos= my_b_tell(to_file);
  strpos= sort_buffer;
  org_max_rows=max_rows= param->max_rows;
  
  set_if_bigger(maxcount, 1);
  
  if (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, 0, 0))
    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 (unique_buff)
  {
    /* 
       Called by Unique::get()
       Copy the first argument to unique_buff for unique removal.
       Store it also in 'to_file'.
    */
    buffpek= (BUFFPEK*) queue_top(&queue);
    memcpy(unique_buff, buffpek->key, rec_length);
    if (min_dupl_count)
      memcpy(&dupl_count, unique_buff+dupl_count_ofs, 
             sizeof(dupl_count));
    buffpek->key+= rec_length;
    if (! --buffpek->mem_count)
    {
      if (!(error= (int) read_to_buffer(from_file, buffpek,
                                        rec_length)))
      {
        (void) queue_remove_top(&queue);
        reuse_freed_buff(&queue, buffpek, rec_length);
      }
      else if (error == -1)
        goto err;                        /* purecov: inspected */ 
    }
    queue_replace_top(&queue);            // Top element has been used
  }
  else
    cmp= 0;                                        // Not unique

  while (queue.elements > 1)
  {
    if (killable && thd->check_killed())
    {
      error= 1; goto err;                        /* purecov: inspected */
    }
    for (;;)
    {
      buffpek= (BUFFPEK*) queue_top(&queue);
      src= buffpek->key;
      if (cmp)                                        // Remove duplicates
      {
        if (!(*cmp)(first_cmp_arg, &unique_buff,
                    (uchar**) &buffpek->key))
	{
          if (min_dupl_count)
	  {
            element_count cnt;
            memcpy(&cnt, (uchar *) buffpek->key+dupl_count_ofs, sizeof(cnt));
            dupl_count+= cnt;
          }
          goto skip_duplicate;
        }
        if (min_dupl_count)
	{
          memcpy(unique_buff+dupl_count_ofs, &dupl_count,
                 sizeof(dupl_count));
        }
	src= unique_buff;
      }
        
      /* 
        Do not write into the output file if this is the final merge called
        for a Unique object used for intersection and dupl_count is less
        than min_dupl_count.
        If the Unique object is used to intersect N sets of unique elements
        then for any element:
        dupl_count >= N <=> the element is occurred in each of these N sets.
      */          
      if (!check_dupl_count || dupl_count >= min_dupl_count)
      {
        if (my_b_write(to_file, src+wr_offset, wr_len))
        {
          error=1; goto err;                        /* purecov: inspected */
        }
      }
      if (cmp)
      {   
        memcpy(unique_buff, (uchar*) buffpek->key, rec_length);
        if (min_dupl_count)
          memcpy(&dupl_count, unique_buff+dupl_count_ofs, 
                 sizeof(dupl_count));
      }
      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_top(&queue);
          reuse_freed_buff(&queue, buffpek, rec_length);
          break;                        /* One buffer have been removed */
        }
        else if (error == -1)
          goto err;                        /* purecov: inspected */
      }
      queue_replace_top(&queue);   	/* Top element has been replaced */
    }
  }
  buffpek= (BUFFPEK*) queue_top(&queue);
  buffpek->base= (uchar*) 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, &unique_buff, (uchar**) &buffpek->key))
    {
      if (min_dupl_count)
      {
        element_count cnt;
        memcpy(&cnt, (uchar *) buffpek->key+dupl_count_ofs, sizeof(cnt));
        dupl_count+= cnt;
      }
      buffpek->key+= rec_length;         
      --buffpek->mem_count;
    }

    if (min_dupl_count)
      memcpy(unique_buff+dupl_count_ofs, &dupl_count,
             sizeof(dupl_count));

    if (!check_dupl_count || dupl_count >= min_dupl_count)
    {
      src= unique_buff;
      if (my_b_write(to_file, src+wr_offset, wr_len))
      {
        error=1; goto err;                        /* purecov: inspected */
      }
      if (!--max_rows)
      {
        error= 0;                               
        goto end;                             
      }
    }   
  }

  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,
                     (size_t)(rec_length*buffpek->mem_count)))
      {
        error= 1; goto err;                        /* purecov: inspected */
      }
    }
    else
    {
      register uchar *end;
      src= buffpek->key+offset;
      for (end= src+buffpek->mem_count*rec_length ;
           src != end ;
           src+= rec_length)
      {
        if (check_dupl_count)
        {
          memcpy((uchar *) &dupl_count, src+dupl_count_ofs, sizeof(dupl_count)); 
          if (dupl_count < min_dupl_count)
	    continue;
        }
        if (my_b_write(to_file, src, wr_len))
        {
          error=1; goto err;                        
        }
      }
    }
  }
  while ((error=(int) read_to_buffer(from_file, buffpek, rec_length))
         != -1 && error != 0);

end:
  lastbuff->count= MY_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) */

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
}


void
Type_handler_string_result::sortlength(THD *thd,
                                       const Type_std_attributes *item,
                                       SORT_FIELD_ATTR *sortorder) const
{
  CHARSET_INFO *cs;
  sortorder->length= item->max_length;
  set_if_smaller(sortorder->length, thd->variables.max_sort_length);
  if (use_strnxfrm((cs= item->collation.collation)))
  {
    sortorder->length= cs->coll->strnxfrmlen(cs, sortorder->length);
  }
  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;
  }
}


void
Type_handler_temporal_result::sortlength(THD *thd,
                                         const Type_std_attributes *item,
                                         SORT_FIELD_ATTR *sortorder) const
{
  sortorder->length= 8; // Sizof intern longlong
}


void
Type_handler_int_result::sortlength(THD *thd,
                                        const Type_std_attributes *item,
                                        SORT_FIELD_ATTR *sortorder) const
{
  sortorder->length= 8; // Sizof intern longlong
}


void
Type_handler_real_result::sortlength(THD *thd,
                                        const Type_std_attributes *item,
                                        SORT_FIELD_ATTR *sortorder) const
{
  sortorder->length= sizeof(double);
}


void
Type_handler_decimal_result::sortlength(THD *thd,
                                        const Type_std_attributes *item,
                                        SORT_FIELD_ATTR *sortorder) const
{
  sortorder->length=
    my_decimal_get_binary_size(item->max_length - (item->decimals ? 1 : 0),
                               item->decimals);  
}


/**
  Calculate length of sort key.

  @param thd			  Thread handler
  @param sortorder		  Order of items to sort
  @param s_length	          Number of items to sort
  @param[out] multi_byte_charset Set to 1 if we are using multi-byte charset
                                 (In which case we have to use strxnfrm())

  @note
    sortorder->length is updated for each sort item.

  @return
    Total length of sort buffer in bytes
*/

static uint
sortlength(THD *thd, SORT_FIELD *sortorder, uint s_length,
           bool *multi_byte_charset)
{
  uint length;
  *multi_byte_charset= 0;

  length=0;
  for (; s_length-- ; sortorder++)
  {
    sortorder->suffix_length= 0;
    if (sortorder->field)
    {
      CHARSET_INFO *cs= sortorder->field->sort_charset();
      sortorder->length= sortorder->field->sort_length();
      if (use_strnxfrm((cs=sortorder->field->sort_charset())))
      {
        *multi_byte_charset= true;
        sortorder->length= cs->coll->strnxfrmlen(cs, sortorder->length);
      }
      if (sortorder->field->maybe_null())
	length++;				// Place for NULL marker
    }
    else
    {
      sortorder->item->sortlength(thd, sortorder->item, sortorder);
      if (use_strnxfrm(sortorder->item->collation.collation))
      {
        *multi_byte_charset= true;
      }
      if (sortorder->item->maybe_null)
	length++;				// Place for NULL marker
    }
    set_if_smaller(sortorder->length, thd->variables.max_sort_length);
    length+=sortorder->length;
  }
  sortorder->field= (Field*) 0;			// end marker
  DBUG_PRINT("info",("sort_length: %d",length));
  return length;
}


/**
  Get descriptors of fields appended to sorted fields and
  calculate its total length.

  The function first finds out what fields are used in the result set.
  Then it calculates the length of the buffer to store the values of
  these fields together with the value of sort values. 
  If the calculated length is not greater than max_length_for_sort_data
  the function allocates memory for an array of descriptors containing
  layouts for the values of the non-sorted fields in the buffer and
  fills them.

  @param thd                 Current thread
  @param ptabfield           Array of references to the table fields
  @param sortlength          Total length of sorted fields
  @param [out] addon_buf     Buffer to us for appended fields

  @note
    The null bits for the appended values are supposed to be put together
    and stored the buffer just ahead of the value of the first field.

  @return
    Pointer to the layout descriptors for the appended fields, if any
  @retval
    NULL   if we do not store field values with sort data.
*/

static SORT_ADDON_FIELD *
get_addon_fields(ulong max_length_for_sort_data,
                 Field **ptabfield, uint sortlength, LEX_STRING *addon_buf)
{
  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;
  DBUG_ENTER("get_addon_fields");

  /*
    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.
    But beware the case when item->cmp_type() != item->result_type()
  */
  addon_buf->str= 0;
  addon_buf->length= 0;

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

  if (length+sortlength > max_length_for_sort_data ||
      !my_multi_malloc(MYF(MY_WME | MY_THREAD_SPECIFIC),
                       &addonf, sizeof(SORT_ADDON_FIELD) * (fields+1),
                       &addon_buf->str, length,
                       NullS))

    DBUG_RETURN(0);

  addon_buf->length= 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));
  DBUG_RETURN(addonf-fields);
}


/**
  Copy (unpack) values appended to sorted fields from a buffer back to
  their regular positions specified by the Field::ptr pointers.

  @param addon_field     Array of descriptors for appended fields
  @param buff            Buffer which to unpack the value from

  @note
    The function is supposed to be used only as a callback function
    when getting field values for the sorted result set.

  @return
    void.
*/

static void 
unpack_addon_fields(struct st_sort_addon_field *addon_field, uchar *buff,
                    uchar *buff_end)
{
  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, buff_end, 0);
  }
}

/*
** 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;
    }
  }
}

/**
   Free SORT_INFO
*/

SORT_INFO::~SORT_INFO()
{
  DBUG_ENTER("~SORT_INFO::SORT_INFO()");
  free_data();
  DBUG_VOID_RETURN;
}
