mariadb/sql/filesort.cc

/* Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB  

   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; either version 2 of the License, or
   (at your option) any later version.

   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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */


/* Sorts a database */

#include "mysql_priv.h"
#ifdef HAVE_STDDEF_H
#include <stddef.h>			/* for macro offsetof */
#endif
#include <m_ctype.h>
#include "sql_sort.h"

#ifndef THREAD
#define SKIP_DBUG_IN_FILESORT
#endif

	/* How to write record_ref. */

#define WRITE_REF(file,from) \
if (my_b_write((file),(byte*) (from),param->ref_length)) \
  DBUG_RETURN(1);

	/* functions defined in this file */

static char **make_char_array(register uint fields, uint length, myf my_flag);
static BUFFPEK *read_buffpek_from_file(IO_CACHE *buffer_file, uint count);
static ha_rows find_all_keys(SORTPARAM *param,SQL_SELECT *select,
			     uchar * *sort_keys, IO_CACHE *buffer_file,
			     IO_CACHE *tempfile,IO_CACHE *indexfile);
static int write_keys(SORTPARAM *param,uchar * *sort_keys,
		      uint count, IO_CACHE *buffer_file, IO_CACHE *tempfile);
static void make_sortkey(SORTPARAM *param,uchar *to, byte *ref_pos);
static int merge_index(SORTPARAM *param,uchar *sort_buffer,
		       BUFFPEK *buffpek,
		       uint maxbuffer,IO_CACHE *tempfile,
		       IO_CACHE *outfile);
static bool save_index(SORTPARAM *param,uchar **sort_keys, uint count);
static uint sortlength(SORT_FIELD *sortorder, uint s_length,
		       bool *multi_byte_charset);
static SORT_ADDON_FIELD *get_addon_fields(THD *thd, Field **ptabfield,
                                          uint sortlength, uint *plength);
static void unpack_addon_fields(struct st_sort_addon_field *addon_field,
                                byte *buff);

	/*
	  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 table->io_cache or
	  table->record_pointers
	*/

ha_rows filesort(THD *thd, TABLE *table, SORT_FIELD *sortorder, uint s_length,
		 SQL_SELECT *select, ha_rows max_rows, ha_rows *examined_rows)
{
  int error;
  ulong memavl, min_sort_memory;
  uint maxbuffer;
  BUFFPEK *buffpek;
  ha_rows records= HA_POS_ERROR;
  uchar **sort_keys;
  IO_CACHE tempfile, buffpek_pointers, *selected_records_file, *outfile; 
  SORTPARAM param;
  bool multi_byte_charset;
  DBUG_ENTER("filesort");
  DBUG_EXECUTE("info",TEST_filesort(sortorder,s_length););
#ifdef SKIP_DBUG_IN_FILESORT
  DBUG_PUSH("");		/* No DBUG here */
#endif

  outfile= table->sort.io_cache;
  my_b_clear(&tempfile);
  my_b_clear(&buffpek_pointers);
  buffpek=0;
  sort_keys= (uchar **) NULL;
  error= 1;
  bzero((char*) &param,sizeof(param));
  param.sort_length= sortlength(sortorder, s_length, &multi_byte_charset);
  param.ref_length= table->file->ref_length;
  param.addon_field= 0;
  param.addon_length= 0;
  if (!(table->tmp_table || table->fulltext_searched))
  {
    /* 
      Get the descriptors of all fields whose values are appended 
      to sorted fields and get its total length in param.spack_length.
    */
    param.addon_field= get_addon_fields(thd, table->field, 
                                        param.sort_length,
                                        &param.addon_length);
  }
  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)
  {
    param.res_length= param.addon_length;
    if (!(table->sort.addon_buf= (byte *) my_malloc(param.addon_length,
                                                    MYF(MY_WME))))
      goto err;
  }
  else
  {
    param.res_length= param.ref_length;
    /* 
      The reference to the record is considered 
      as an additional sorted field
    */
    param.sort_length+= param.ref_length;
  }
  param.rec_length= param.sort_length+param.addon_length;
  param.max_rows= max_rows;

  if (select && select->quick)
  {
    statistic_increment(filesort_range_count, &LOCK_status);
  }
  else
  {
    statistic_increment(filesort_scan_count, &LOCK_status);
  }
#ifdef CAN_TRUST_RANGE
  if (select && select->quick && select->quick->records > 0L)
  {
    records=min((ha_rows) (select->quick->records*2+EXTRA_RECORDS*2),
		table->file->records)+EXTRA_RECORDS;
    selected_records_file=0;
  }
  else
#endif
  {
    records=table->file->estimate_number_of_rows();
    selected_records_file= 0;
  }
  if (param.rec_length == param.ref_length && records > param.max_rows)
    records=param.max_rows;			/* purecov: inspected */

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

  memavl= thd->variables.sortbuff_size;
  min_sort_memory= max(MIN_SORT_MEMORY, param.sort_length*MERGEBUFF2);
  while (memavl >= min_sort_memory)
  {
    ulong old_memavl;
    ulong keys= memavl/(param.rec_length+sizeof(char*));
    param.keys=(uint) min(records+1, keys);
    if ((sort_keys= (uchar **) make_char_array(param.keys, param.rec_length,
					       MYF(0))))
      break;
    old_memavl=memavl;
    if ((memavl=memavl/4*3) < min_sort_memory && old_memavl > min_sort_memory)
      memavl= min_sort_memory;
  }
  if (memavl < min_sort_memory)
  {
    my_error(ER_OUTOFMEMORY,MYF(ME_ERROR+ME_WAITTANG),
	     thd->variables.sortbuff_size);
    goto err;
  }
  if (open_cached_file(&buffpek_pointers,mysql_tmpdir,TEMP_PREFIX,
		       DISK_BUFFER_SIZE, MYF(MY_WME)))
    goto err;

  param.keys--;
  param.sort_form= table;
  param.end=(param.local_sortorder=sortorder)+s_length;
  if ((records=find_all_keys(&param,select,sort_keys, &buffpek_pointers,
			     &tempfile, selected_records_file)) ==
      HA_POS_ERROR)
    goto err;
  maxbuffer= (uint) (my_b_tell(&buffpek_pointers)/sizeof(*buffpek));

  if (maxbuffer == 0)			// The whole set is in memory
  {
    if (save_index(&param,sort_keys,(uint) records))
      goto err;
  }
  else
  {
    if (!(buffpek=read_buffpek_from_file(&buffpek_pointers, maxbuffer)))
      goto err;
    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;
    reinit_io_cache(outfile,WRITE_CACHE,0L,0,0);

    /*
      Use also the space previously used by string pointers in sort_buffer
      for temporary key storage.
    */
    param.keys=((param.keys*(param.rec_length+sizeof(char*))) /
		param.rec_length-1);
    maxbuffer--;				// Offset from 0
    if (merge_many_buff(&param,(uchar*) 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_keys,buffpek,maxbuffer,&tempfile,
		    outfile))
      goto err;
  }
  if (records > param.max_rows)
    records=param.max_rows;
  error =0;

 err:
  if (param.tmp_buffer)
    x_free(param.tmp_buffer);
  x_free((gptr) sort_keys);
  x_free((gptr) buffpek);
  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)
    my_error(ER_FILSORT_ABORT,MYF(ME_ERROR+ME_WAITTANG));
  else
    statistic_add(filesort_rows, (ulong) records, &LOCK_status);
  *examined_rows= param.examined_rows;
#ifdef SKIP_DBUG_IN_FILESORT
  DBUG_POP();			/* Ok to DBUG */
#endif
  DBUG_PRINT("exit",("records: %ld",records));
  DBUG_RETURN(error ? HA_POS_ERROR : records);
} /* filesort */


void filesort_free_buffers(TABLE *table)
{
  if (table->sort.record_pointers)
  {
    my_free((gptr) table->sort.record_pointers,MYF(0));
    table->sort.record_pointers=0;
  }
  if (table->sort.addon_buf)
  {
    my_free((char *) table->sort.addon_buf, MYF(0));
    my_free((char *) table->sort.addon_field, MYF(MY_ALLOW_ZERO_PTR));
    table->sort.addon_buf=0;
    table->sort.addon_field=0;
  }
}

	/* Make a array of string pointers */

static char **make_char_array(register uint fields, uint length, myf my_flag)
{
  register char **pos;
  char **old_pos,*char_pos;
  DBUG_ENTER("make_char_array");

  if ((old_pos= (char**) my_malloc((uint) fields*(length+sizeof(char*)),
				    my_flag)))
  {
    pos=old_pos; char_pos=((char*) (pos+fields)) -length;
    while (fields--) *(pos++) = (char_pos+= length);
  }

  DBUG_RETURN(old_pos);
} /* make_char_array */


	/* Read all buffer pointers into memory */

static BUFFPEK *read_buffpek_from_file(IO_CACHE *buffpek_pointers, uint count)
{
  ulong length;
  BUFFPEK *tmp;
  DBUG_ENTER("read_buffpek_from_file");
  tmp=(BUFFPEK*) my_malloc(length=sizeof(BUFFPEK)*count, MYF(MY_WME));
  if (tmp)
  {
    if (reinit_io_cache(buffpek_pointers,READ_CACHE,0L,0,0) ||
	my_b_read(buffpek_pointers, (byte*) tmp, length))
    {
      my_free((char*) tmp, MYF(0));
      tmp=0;
    }      
  }
  DBUG_RETURN(tmp);
}



	/* Search after sort_keys and place them in a temp. file */

static ha_rows find_all_keys(SORTPARAM *param, SQL_SELECT *select,
			     uchar **sort_keys,
			     IO_CACHE *buffpek_pointers,
			     IO_CACHE *tempfile, IO_CACHE *indexfile)
{
  int error,flag,quick_select;
  uint idx,indexpos,ref_length;
  byte *ref_pos,*next_pos,ref_buff[MAX_REFLENGTH];
  my_off_t record;
  TABLE *sort_form;
  volatile bool *killed= &current_thd->killed;
  handler *file;
  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;
  flag= ((!indexfile && file->table_flags() & HA_REC_NOT_IN_SEQ)
	 || quick_select);
  if (indexfile || flag)
    ref_pos= &file->ref[0];
  next_pos=ref_pos;
  if (! indexfile && ! quick_select)
  {
    file->reset();			// QQ; Shouldn't be needed
    if (sort_form->key_read)		// QQ Can be removed after the reset
      file->extra(HA_EXTRA_KEYREAD);	// QQ is removed
    next_pos=(byte*) 0;			/* Find records in sequence */
    file->rnd_init();
    file->extra_opt(HA_EXTRA_CACHE,
		    current_thd->variables.read_buff_size);
  }

  for (;;)
  {
    if (quick_select)
    {
      if ((error=select->quick->get_next()))
	break;
      file->position(sort_form->record[0]);
    }
    else					/* Not quick-select */
    {
      if (indexfile)
      {
	if (my_b_read(indexfile,(byte*) ref_pos,ref_length)) /* purecov: deadcode */
	{
	  error= my_errno ? my_errno : -1;		/* Abort */
	  break;
	}
	error=file->rnd_pos(sort_form->record[0],next_pos);
      }
      else
      {
	error=file->rnd_next(sort_form->record[0]);
	if (!flag)
	{
	  ha_store_ptr(ref_pos,ref_length,record); // Position to row
	  record+=sort_form->db_record_offset;
	}
	else
	  file->position(sort_form->record[0]);
      }
      if (error && error != HA_ERR_RECORD_DELETED)
	break;
    }
    if (*killed)
    {
      DBUG_PRINT("info",("Sort killed by user"));
      (void) file->extra(HA_EXTRA_NO_CACHE);
      file->rnd_end();
      DBUG_RETURN(HA_POS_ERROR);		/* purecov: inspected */
    }
    if (error == 0)
      param->examined_rows++;
    if (error == 0 && (!select || select->skipp_record() == 0))
    {
      if (idx == param->keys)
      {
	if (write_keys(param,sort_keys,idx,buffpek_pointers,tempfile))
	  DBUG_RETURN(HA_POS_ERROR);
	idx=0;
	if (param->ref_length == param->rec_length &&
	    my_b_tell(tempfile)/param->rec_length >= param->max_rows)
	{
	  /*
	    We are writing the result index file and have found all
	    rows that we need.  Abort the sort and return the result.
	  */
	  error=HA_ERR_END_OF_FILE;
	  break;			/* Found enough records */
	}
	indexpos++;
      }
      make_sortkey(param,sort_keys[idx++],ref_pos);
    }
    else
      file->unlock_row();
  }
  (void) file->extra(HA_EXTRA_NO_CACHE);	/* End cacheing of records */
  file->rnd_end();
  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,sort_keys,idx,buffpek_pointers,tempfile))
    DBUG_RETURN(HA_POS_ERROR);			/* purecov: inspected */
  DBUG_RETURN(my_b_inited(tempfile) ?
	      (ha_rows) (my_b_tell(tempfile)/param->rec_length) :
	      idx);
} /* find_all_keys */


	/* Skriver en buffert med nycklar till filen */

static int
write_keys(SORTPARAM *param, register uchar **sort_keys, uint count,
           IO_CACHE *buffpek_pointers, IO_CACHE *tempfile)
{
  uint sort_length, rec_length;
  uchar **end;
  BUFFPEK buffpek;
  DBUG_ENTER("write_keys");

  sort_length= param->sort_length;
  rec_length= param->rec_length;
#ifdef MC68000
  quicksort(sort_keys,count,sort_length);
#else
  my_string_ptr_sort((gptr) sort_keys, (uint) count, sort_length);
#endif
  if (!my_b_inited(tempfile) &&
      open_cached_file(tempfile, mysql_tmpdir, TEMP_PREFIX, DISK_BUFFER_SIZE,
                       MYF(MY_WME)))
    goto err;                                        /* purecov: inspected */
  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, (byte*) *sort_keys, (uint) rec_length))
      goto err;
  if (my_b_write(buffpek_pointers, (byte*) &buffpek, sizeof(buffpek)))
    goto err;
  DBUG_RETURN(0);

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


	/* makes a sort-key from record */

static void make_sortkey(register SORTPARAM *param,
			 register uchar *to, byte *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
      if (field->maybe_null())
      {
	if (field->is_null())
	{
	  if (sort_field->reverse)
	    bfill(to,sort_field->length+1,(char) 255);
	  else
	    bzero((char*) to,sort_field->length+1);
	  to+= sort_field->length+1;
	  continue;
	}
	else
	  *to++=1;
      }
      field->sort_string((char*) to,sort_field->length);
    }
    else
    {						// Item
      Item *item=sort_field->item;
      switch (sort_field->result_type) {
      case STRING_RESULT:
	{
          CHARSET_INFO *cs=item->charset();
	  if ((maybe_null=item->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->val_str(&tmp);
	  if (!res)
	  {
	    if (item->maybe_null)
	      bzero((char*) to-1,sort_field->length+1);
	    else
	    {
	      DBUG_PRINT("warning",
			 ("Got null on something that shouldn't be null"));
	      bzero((char*) to,sort_field->length);	// Avoid crash
	    }
	    break;
	  }
	  length=res->length();
	  int diff=(int) (sort_field->length-length);
	  if (diff < 0)
	  {
	    diff=0;				/* purecov: inspected */
	    length=sort_field->length;
	  }
          if (sort_field->need_strxnfrm)
          {
	    char *from=(char*) res->ptr();
	    if ((unsigned char *)from == to)
	    {
	      set_if_smaller(length,sort_field->length);
	      memcpy(param->tmp_buffer,from,length);
	      from=param->tmp_buffer;
	    }
	    uint tmp_length=my_strnxfrm(cs,to,sort_field->length,
					(unsigned char *) from, length);
	    if (tmp_length < sort_field->length)
	      bzero((char*) to+tmp_length,sort_field->length-tmp_length);
          }
          else
          {
             my_strnxfrm(cs,(uchar*)to,length,(const uchar*)res->ptr(),length);
             bzero((char *)to+length,diff);
          }
		break;
	}
      case INT_RESULT:
	{
	  longlong value=item->val_int();
	  if ((maybe_null=item->maybe_null))
	    *to++=1;				/* purecov: inspected */
	  if (item->null_value)
	  {
	    if (item->maybe_null)
	      bzero((char*) to-1,sort_field->length+1);
	    else
	    {
	      DBUG_PRINT("warning",
			 ("Got null on something that shouldn't be null"));
	      bzero((char*) to,sort_field->length);
	    }
	    break;
	  }
#if SIZEOF_LONG_LONG > 4
	  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);
	  to[0]= (uchar) (value >> 56) ^ 128;	// Fix sign
#else
	  to[3]= (uchar) value;
	  to[2]= (uchar) (value >> 8);
	  to[1]= (uchar) (value >> 16);
	  to[0]= (uchar) (value >> 24) ^ 128;	// Fix sign
#endif
	  break;
	}
      case REAL_RESULT:
	{
	  double value=item->val();
	  if ((maybe_null=item->null_value))
	  {
	    bzero((char*) to,sort_field->length+1);
	    to++;
	    break;
	  }
	  if ((maybe_null=item->maybe_null))
	    *to++=1;
	  change_double_for_sort(value,(byte*) 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];
      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);
    bzero((char *) nulls, addonf->offset);
    to+= addonf->offset;
    for ( ; (field= addonf->field) ; addonf++)
    {
      if (addonf->null_bit && field->is_null())
        nulls[addonf->null_offset]|= addonf->null_bit;
      else
        field->pack((char *) to, field->ptr);
      to+= addonf->length;
    }
  }
  else
  {
    /* Save filepos last */
    memcpy((byte*) to, ref_pos, (size_s) param->ref_length);
  }
  return;
}


static bool save_index(SORTPARAM *param, uchar **sort_keys, uint count)
{
  uint offset,res_length;
  byte *to;
  DBUG_ENTER("save_index");

  my_string_ptr_sort((gptr) sort_keys, (uint) count, param->sort_length);
  res_length= param->res_length;
  offset= param->rec_length-res_length;
  if ((ha_rows) count > param->max_rows)
    count=(uint) param->max_rows;
  if (!(to= param->sort_form->sort.record_pointers=
        (byte*) my_malloc(res_length*count, MYF(MY_WME))))
    DBUG_RETURN(1);                 /* purecov: inspected */
  for (uchar **end= sort_keys+count ; sort_keys != end ; sort_keys++)
  {
    memcpy(to, *sort_keys+offset, res_length);
    to+= res_length;
  }
  DBUG_RETURN(0);
}


	/* Merge buffers to make < MERGEBUFF2 buffers */

int merge_many_buff(SORTPARAM *param, uchar *sort_buffer,
		    BUFFPEK *buffpek, uint *maxbuffer, IO_CACHE *t_file)
{
  register int 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)
  {
    reinit_io_cache(from_file,READ_CACHE,0L,0,0);
    reinit_io_cache(to_file,WRITE_CACHE,0L,0,0);
    lastbuff=buffpek;
    for (i=0 ; i <= (int) *maxbuffer-MERGEBUFF*3/2 ; i+=MERGEBUFF)
    {
      if (merge_buffers(param,from_file,to_file,sort_buffer,lastbuff++,
			buffpek+i,buffpek+i+MERGEBUFF-1,0))
	break;					/* purecov: inspected */
    }
    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;
  }
  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 */
	/* This returns (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) min((ha_rows) buffpek->max_keys,buffpek->count)))
  {
    if (my_pread(fromfile->file,(byte*) 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 */


/* 
   Merge buffers to one buffer 
*/

int merge_buffers(SORTPARAM *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,sort_length,res_length,offset;
  ulong maxcount;
  ha_rows max_rows,org_max_rows;
  my_off_t to_start_filepos;
  uchar *strpos;
  BUFFPEK *buffpek,**refpek;
  QUEUE queue;
  qsort2_cmp cmp;
  volatile bool *killed= &current_thd->killed;
  bool not_killable;
  DBUG_ENTER("merge_buffers");

  statistic_increment(filesort_merge_passes, &LOCK_status);
  if (param->not_killable)
  {
    killed= &not_killable;
    not_killable= 0;
  }

  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->keys/((uint) (Tb-Fb) +1));
  to_start_filepos= my_b_tell(to_file);
  strpos= (uchar*) sort_buffer;
  org_max_rows=max_rows= param->max_rows;

  if (init_queue(&queue, (uint) (Tb-Fb)+1, offsetof(BUFFPEK,key), 0,
                 (queue_compare) (cmp= get_ptr_compare(sort_length)),
                 (void*) &sort_length))
    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 */
    queue_insert(&queue, (byte*) 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, (byte*) 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)(&sort_length, &(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,(byte*) buffpek->key, rec_length))
        {
          error=1; goto err;                        /* purecov: inspected */
        }
      }
      else
      {
        if (my_b_write(to_file, (byte*) 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)))
        {
          uchar *base= buffpek->base;
          ulong max_keys= buffpek->max_keys;

          VOID(queue_remove(&queue,0));

          /* Put room used by buffer to use in other buffer */
          for (refpek= (BUFFPEK**) &queue_top(&queue);
               refpek <= (BUFFPEK**) &queue_end(&queue);
               refpek++)
          {
            buffpek= *refpek;
            if (buffpek->base+buffpek->max_keys*rec_length == base)
            {
              buffpek->max_keys+= max_keys;
              break;
            }
            else if (base+max_keys*rec_length == buffpek->base)
            {
              buffpek->base= base;
              buffpek->max_keys+= max_keys;
              break;
            }
          }
          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->keys;

  /*
    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)(&sort_length, &(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,(byte*) 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, (byte *) 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(SORTPARAM *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 */


/*
  Calculate length of sort key

  SYNOPSIS
    sortlength()
    sortorder		Order of items to sort
    uint s_length	Number of items to sort
    multi_byte_charset  (out)
			Set to 1 if we are using multi-byte charset
			(In which case we have to use strxnfrm())

  NOTES
    sortorder->length is updated for each sort item
    sortorder->need_strxnfrm is set 1 if we have to use strxnfrm

  RETURN
    Total length of sort buffer in bytes
*/

static uint
sortlength(SORT_FIELD *sortorder, uint s_length, bool *multi_byte_charset)
{
  reg2 uint length;
  THD *thd= current_thd;
  CHARSET_INFO *cs;
  *multi_byte_charset= 0;

  length=0;
  for (; s_length-- ; sortorder++)
  {
    sortorder->need_strxnfrm= 0;
    if (sortorder->field)
    {
      if (sortorder->field->type() == FIELD_TYPE_BLOB)
	sortorder->length= thd->variables.max_sort_length;
      else
      {
	sortorder->length=sortorder->field->pack_length();
	if (use_strnxfrm((cs=sortorder->field->charset())))
	{
	  sortorder->need_strxnfrm= 1;
	  *multi_byte_charset= 1;
	  sortorder->length= sortorder->length*cs->strxfrm_multiply;
	}
      }
      if (sortorder->field->maybe_null())
	length++;				// Place for NULL marker
    }
    else
    {
      switch ((sortorder->result_type=sortorder->item->result_type())) {
      case STRING_RESULT:
	sortorder->length=sortorder->item->max_length;
	if (use_strnxfrm((cs=sortorder->item->charset())))
	{ 
	  sortorder->length= sortorder->length*cs->strxfrm_multiply;
	  sortorder->need_strxnfrm= 1;
	  *multi_byte_charset= 1;
	}
	break;
      case INT_RESULT:
#if SIZEOF_LONG_LONG > 4
	sortorder->length=8;			// Size of intern longlong
#else
	sortorder->length=4;
#endif
	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)
	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

  SYNOPSIS
    get_addon_fields()
    thd                 Current thread
    ptabfields          Array of references to the table fields
    sortlength          Total length of sorted fields
    plength    out:     Total length of appended fields

  DESCRIPTION
    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.

  NOTES
    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
    NULL - if we do not store field values with sort data.
*/

static SORT_ADDON_FIELD *
get_addon_fields(THD *thd, Field **ptabfield, uint sortlength, uint *plength)
{
  Field **pfield;
  Field *field;
  SORT_ADDON_FIELD *addonf;
  uint length= 0;
  uint fields= 0;
  uint null_fields= 0;

  /* 
     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;
  /*
     The following statement is added to avoid sorting in alter_table.
     The fact is the filter 'field->query_id != thd->query_id'
     doesn't work for alter table
  */
  if (thd->lex.sql_command != SQLCOM_SELECT)
    return 0;
  for (pfield= ptabfield; (field= *pfield) ; pfield++)
  {
    if (field->query_id != thd->query_id)
      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 > thd->variables.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 (field->query_id != thd->query_id)
      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);
}


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

  SYNOPSIS
    unpack_addon_fields()
    addon_field     Array of descriptors for appended fields
    buff            Buffer which to unpack the value from

  NOTES
    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, byte *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, (char *) 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,byte *to)
{
  uchar *tmp=(uchar*) to;
  if (nr == 0.0)
  {						/* Change to zero string */
    tmp[0]=(uchar) 128;
    bzero((char*) tmp+1,sizeof(nr)-1);
  }
  else
  {
#ifdef WORDS_BIGENDIAN
    memcpy_fixed(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;
    }
  }
}