summaryrefslogtreecommitdiff
path: root/sql/uniques.cc
blob: 690b310bde5ee88392eefd2c388cfc267d6a6eed (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
/* Copyright (C) 2001 MySQL 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; 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

/*
  Function to handle quick removal of duplicates
  This code is used when doing multi-table deletes to find the rows in
  reference tables that needs to be deleted.

  The basic idea is as follows:

  Store first all strings in a binary tree, ignoring duplicates.
  When the tree uses more memory than 'max_heap_table_size',
  write the tree (in sorted order) out to disk and start with a new tree.
  When all data has been generated, merge the trees (removing any found
  duplicates).

  The unique entries will be returned in sort order, to ensure that we do the
  deletes in disk order.
*/

#include "sql_priv.h"
#include "unireg.h"
#include "sql_sort.h"
#include "queues.h"                             // QUEUE
#include "my_tree.h"                            // element_count
#include "sql_class.h"                          // Unique

int unique_write_to_file(uchar* key, element_count count, Unique *unique)
{
  /*
    Use unique->size (size of element stored in the tree) and not
    unique->tree.size_of_element. The latter is different from unique->size
    when tree implementation chooses to store pointer to key in TREE_ELEMENT
    (instead of storing the element itself there)
  */
  return my_b_write(&unique->file, key, unique->size) ? 1 : 0;
}

int unique_write_to_ptrs(uchar* key, element_count count, Unique *unique)
{
  memcpy(unique->record_pointers, key, unique->size);
  unique->record_pointers+=unique->size;
  return 0;
}

Unique::Unique(qsort_cmp2 comp_func, void * comp_func_fixed_arg,
	       uint size_arg, ulonglong max_in_memory_size_arg)
  :max_in_memory_size(max_in_memory_size_arg), size(size_arg), elements(0)
{
  my_b_clear(&file);
  init_tree(&tree, (ulong) (max_in_memory_size / 16), 0, size, comp_func, 0,
            NULL, comp_func_fixed_arg);
  /* If the following fail's the next add will also fail */
  my_init_dynamic_array(&file_ptrs, sizeof(BUFFPEK), 16, 16);
  /*
    If you change the following, change it in get_max_elements function, too.
  */
  max_elements= (ulong) (max_in_memory_size /
                         ALIGN_SIZE(sizeof(TREE_ELEMENT)+size));
  (void) open_cached_file(&file, mysql_tmpdir,TEMP_PREFIX, DISK_BUFFER_SIZE,
		   MYF(MY_WME));
}


/*
  Calculate log2(n!)

  NOTES
    Stirling's approximate formula is used:

      n! ~= sqrt(2*M_PI*n) * (n/M_E)^n

    Derivation of formula used for calculations is as follows:

    log2(n!) = log(n!)/log(2) = log(sqrt(2*M_PI*n)*(n/M_E)^n) / log(2) =

      = (log(2*M_PI*n)/2 + n*log(n/M_E)) / log(2).
*/

inline double log2_n_fact(double x)
{
  return (log(2*M_PI*x)/2 + x*log(x/M_E)) / M_LN2;
}


/*
  Calculate cost of merge_buffers function call for given sequence of
  input stream lengths and store the number of rows in result stream in *last.

  SYNOPSIS
    get_merge_buffers_cost()
      buff_elems  Array of #s of elements in buffers
      elem_size   Size of element stored in buffer
      first       Pointer to first merged element size
      last        Pointer to last merged element size

  RETURN
    Cost of merge_buffers operation in disk seeks.

  NOTES
    It is assumed that no rows are eliminated during merge.
    The cost is calculated as

      cost(read_and_write) + cost(merge_comparisons).

    All bytes in the sequences is read and written back during merge so cost
    of disk io is 2*elem_size*total_buf_elems/IO_SIZE (2 is for read + write)

    For comparisons cost calculations we assume that all merged sequences have
    the same length, so each of total_buf_size elements will be added to a sort
    heap with (n_buffers-1) elements. This gives the comparison cost:

      total_buf_elems* log2(n_buffers) / TIME_FOR_COMPARE_ROWID;
*/

static double get_merge_buffers_cost(uint *buff_elems, uint elem_size,
                                     uint *first, uint *last)
{
  uint total_buf_elems= 0;
  for (uint *pbuf= first; pbuf <= last; pbuf++)
    total_buf_elems+= *pbuf;
  *last= total_buf_elems;

  size_t n_buffers= last - first + 1;

  /* Using log2(n)=log(n)/log(2) formula */
  return 2*((double)total_buf_elems*elem_size) / IO_SIZE +
     total_buf_elems*log((double) n_buffers) / (TIME_FOR_COMPARE_ROWID * M_LN2);
}


/*
  Calculate cost of merging buffers into one in Unique::get, i.e. calculate
  how long (in terms of disk seeks) the two calls
    merge_many_buffs(...);
    merge_buffers(...);
  will take.

  SYNOPSIS
    get_merge_many_buffs_cost()
      buffer        buffer space for temporary data, at least
                    Unique::get_cost_calc_buff_size bytes
      maxbuffer     # of full buffers
      max_n_elems   # of elements in first maxbuffer buffers
      last_n_elems  # of elements in last buffer
      elem_size     size of buffer element

  NOTES
    maxbuffer+1 buffers are merged, where first maxbuffer buffers contain
    max_n_elems elements each and last buffer contains last_n_elems elements.

    The current implementation does a dumb simulation of merge_many_buffs
    function actions.

  RETURN
    Cost of merge in disk seeks.
*/

static double get_merge_many_buffs_cost(uint *buffer,
                                        uint maxbuffer, uint max_n_elems,
                                        uint last_n_elems, int elem_size)
{
  register int i;
  double total_cost= 0.0;
  uint *buff_elems= buffer; /* #s of elements in each of merged sequences */

  /*
    Set initial state: first maxbuffer sequences contain max_n_elems elements
    each, last sequence contains last_n_elems elements.
  */
  for (i = 0; i < (int)maxbuffer; i++)
    buff_elems[i]= max_n_elems;
  buff_elems[maxbuffer]= last_n_elems;

  /*
    Do it exactly as merge_many_buff function does, calling
    get_merge_buffers_cost to get cost of merge_buffers.
  */
  if (maxbuffer >= MERGEBUFF2)
  {
    while (maxbuffer >= MERGEBUFF2)
    {
      uint lastbuff= 0;
      for (i = 0; i <= (int) maxbuffer - MERGEBUFF*3/2; i += MERGEBUFF)
      {
        total_cost+=get_merge_buffers_cost(buff_elems, elem_size,
                                           buff_elems + i,
                                           buff_elems + i + MERGEBUFF-1);
	lastbuff++;
      }
      total_cost+=get_merge_buffers_cost(buff_elems, elem_size,
                                         buff_elems + i,
                                         buff_elems + maxbuffer);
      maxbuffer= lastbuff;
    }
  }

  /* Simulate final merge_buff call. */
  total_cost += get_merge_buffers_cost(buff_elems, elem_size,
                                       buff_elems, buff_elems + maxbuffer);
  return total_cost;
}


/*
  Calculate cost of using Unique for processing nkeys elements of size
  key_size using max_in_memory_size memory.

  SYNOPSIS
    Unique::get_use_cost()
      buffer    space for temporary data, use Unique::get_cost_calc_buff_size
                to get # bytes needed.
      nkeys     #of elements in Unique
      key_size  size of each elements in bytes
      max_in_memory_size amount of memory Unique will be allowed to use

  RETURN
    Cost in disk seeks.

  NOTES
    cost(using_unqiue) =
      cost(create_trees) +  (see #1)
      cost(merge) +         (see #2)
      cost(read_result)     (see #3)

    1. Cost of trees creation
      For each Unique::put operation there will be 2*log2(n+1) elements
      comparisons, where n runs from 1 tree_size (we assume that all added
      elements are different). Together this gives:

      n_compares = 2*(log2(2) + log2(3) + ... + log2(N+1)) = 2*log2((N+1)!)

      then cost(tree_creation) = n_compares*ROWID_COMPARE_COST;

      Total cost of creating trees:
      (n_trees - 1)*max_size_tree_cost + non_max_size_tree_cost.

      Approximate value of log2(N!) is calculated by log2_n_fact function.

    2. Cost of merging.
      If only one tree is created by Unique no merging will be necessary.
      Otherwise, we model execution of merge_many_buff function and count
      #of merges. (The reason behind this is that number of buffers is small,
      while size of buffers is big and we don't want to loose precision with
      O(x)-style formula)

    3. If only one tree is created by Unique no disk io will happen.
      Otherwise, ceil(key_len*n_keys) disk seeks are necessary. We assume
      these will be random seeks.
*/

double Unique::get_use_cost(uint *buffer, uint nkeys, uint key_size,
                            ulonglong max_in_memory_size)
{
  ulong max_elements_in_tree;
  ulong last_tree_elems;
  int   n_full_trees; /* number of trees in unique - 1 */
  double result;

  max_elements_in_tree= ((ulong) max_in_memory_size /
                         ALIGN_SIZE(sizeof(TREE_ELEMENT)+key_size));

  n_full_trees=    nkeys / max_elements_in_tree;
  last_tree_elems= nkeys % max_elements_in_tree;

  /* Calculate cost of creating trees */
  result= 2*log2_n_fact(last_tree_elems + 1.0);
  if (n_full_trees)
    result+= n_full_trees * log2_n_fact(max_elements_in_tree + 1.0);
  result /= TIME_FOR_COMPARE_ROWID;

  DBUG_PRINT("info",("unique trees sizes: %u=%u*%lu + %lu", nkeys,
                     n_full_trees, n_full_trees?max_elements_in_tree:0,
                     last_tree_elems));

  if (!n_full_trees)
    return result;

  /*
    There is more then one tree and merging is necessary.
    First, add cost of writing all trees to disk, assuming that all disk
    writes are sequential.
  */
  result += DISK_SEEK_BASE_COST * n_full_trees *
              ceil(((double) key_size)*max_elements_in_tree / IO_SIZE);
  result += DISK_SEEK_BASE_COST * ceil(((double) key_size)*last_tree_elems / IO_SIZE);

  /* Cost of merge */
  double merge_cost= get_merge_many_buffs_cost(buffer, n_full_trees,
                                               max_elements_in_tree,
                                               last_tree_elems, key_size);
  if (merge_cost < 0.0)
    return merge_cost;

  result += merge_cost;
  /*
    Add cost of reading the resulting sequence, assuming there were no
    duplicate elements.
  */
  result += ceil((double)key_size*nkeys/IO_SIZE);

  return result;
}

Unique::~Unique()
{
  close_cached_file(&file);
  delete_tree(&tree);
  delete_dynamic(&file_ptrs);
}


    /* Write tree to disk; clear tree */
bool Unique::flush()
{
  BUFFPEK file_ptr;
  elements+= tree.elements_in_tree;
  file_ptr.count=tree.elements_in_tree;
  file_ptr.file_pos=my_b_tell(&file);

  if (tree_walk(&tree, (tree_walk_action) unique_write_to_file,
		(void*) this, left_root_right) ||
      insert_dynamic(&file_ptrs, (uchar*) &file_ptr))
    return 1;
  delete_tree(&tree);
  return 0;
}


/*
  Clear the tree and the file.
  You must call reset() if you want to reuse Unique after walk().
*/

void
Unique::reset()
{
  reset_tree(&tree);
  /*
    If elements != 0, some trees were stored in the file (see how
    flush() works). Note, that we can not count on my_b_tell(&file) == 0
    here, because it can return 0 right after walk(), and walk() does not
    reset any Unique member.
  */
  if (elements)
  {
    reset_dynamic(&file_ptrs);
    reinit_io_cache(&file, WRITE_CACHE, 0L, 0, 1);
  }
  elements= 0;
}

/*
  The comparison function, passed to queue_init() in merge_walk() and in
  merge_buffers() when the latter is called from Uniques::get() must
  use comparison function of Uniques::tree, but compare members of struct
  BUFFPEK.
*/

C_MODE_START

static int buffpek_compare(void *arg, uchar *key_ptr1, uchar *key_ptr2)
{
  BUFFPEK_COMPARE_CONTEXT *ctx= (BUFFPEK_COMPARE_CONTEXT *) arg;
  return ctx->key_compare(ctx->key_compare_arg,
                          *((uchar **) key_ptr1), *((uchar **)key_ptr2));
}

C_MODE_END


/*
  DESCRIPTION

    Function is very similar to merge_buffers, but instead of writing sorted
    unique keys to the output file, it invokes walk_action for each key.
    This saves I/O if you need to pass through all unique keys only once.

  SYNOPSIS
    merge_walk()
  All params are 'IN' (but see comment for begin, end):
    merge_buffer       buffer to perform cached piece-by-piece loading
                       of trees; initially the buffer is empty
    merge_buffer_size  size of merge_buffer. Must be aligned with
                       key_length
    key_length         size of tree element; key_length * (end - begin)
                       must be less or equal than merge_buffer_size.
    begin              pointer to BUFFPEK struct for the first tree.
    end                pointer to BUFFPEK struct for the last tree;
                       end > begin and [begin, end) form a consecutive
                       range. BUFFPEKs structs in that range are used and
                       overwritten in merge_walk().
    walk_action        element visitor. Action is called for each unique
                       key.
    walk_action_arg    argument to walk action. Passed to it on each call.
    compare            elements comparison function
    compare_arg        comparison function argument
    file               file with all trees dumped. Trees in the file
                       must contain sorted unique values. Cache must be
                       initialized in read mode.
  RETURN VALUE
    0     ok
    <> 0  error
*/

static bool merge_walk(uchar *merge_buffer, ulong merge_buffer_size,
                       uint key_length, BUFFPEK *begin, BUFFPEK *end,
                       tree_walk_action walk_action, void *walk_action_arg,
                       qsort_cmp2 compare, void *compare_arg,
                       IO_CACHE *file)
{
  BUFFPEK_COMPARE_CONTEXT compare_context = { compare, compare_arg };
  QUEUE queue;
  if (end <= begin ||
      merge_buffer_size < (ulong) (key_length * (end - begin + 1)) ||
      init_queue(&queue, (uint) (end - begin), offsetof(BUFFPEK, key), 0,
                 buffpek_compare, &compare_context))
    return 1;
  /* we need space for one key when a piece of merge buffer is re-read */
  merge_buffer_size-= key_length;
  uchar *save_key_buff= merge_buffer + merge_buffer_size;
  uint max_key_count_per_piece= (uint) (merge_buffer_size/(end-begin) /
                                        key_length);
  /* if piece_size is aligned reuse_freed_buffer will always hit */
  uint piece_size= max_key_count_per_piece * key_length;
  uint bytes_read;               /* to hold return value of read_to_buffer */
  BUFFPEK *top;
  int res= 1;
  /*
    Invariant: queue must contain top element from each tree, until a tree
    is not completely walked through.
    Here we're forcing the invariant, inserting one element from each tree
    to the queue.
  */
  for (top= begin; top != end; ++top)
  {
    top->base= merge_buffer + (top - begin) * piece_size;
    top->max_keys= max_key_count_per_piece;
    bytes_read= read_to_buffer(file, top, key_length);
    if (bytes_read == (uint) (-1))
      goto end;
    DBUG_ASSERT(bytes_read);
    queue_insert(&queue, (uchar *) top);
  }
  top= (BUFFPEK *) queue_top(&queue);
  while (queue.elements > 1)
  {
    /*
      Every iteration one element is removed from the queue, and one is
      inserted by the rules of the invariant. If two adjacent elements on
      the top of the queue are not equal, biggest one is unique, because all
      elements in each tree are unique. Action is applied only to unique
      elements.
    */
    void *old_key= top->key;
    /*
      read next key from the cache or from the file and push it to the
      queue; this gives new top.
    */
    top->key+= key_length;
    if (--top->mem_count)
      queue_replaced(&queue);
    else /* next piece should be read */
    {
      /* save old_key not to overwrite it in read_to_buffer */
      memcpy(save_key_buff, old_key, key_length);
      old_key= save_key_buff;
      bytes_read= read_to_buffer(file, top, key_length);
      if (bytes_read == (uint) (-1))
        goto end;
      else if (bytes_read > 0)      /* top->key, top->mem_count are reset */
        queue_replaced(&queue);     /* in read_to_buffer */
      else
      {
        /*
          Tree for old 'top' element is empty: remove it from the queue and
          give all its memory to the nearest tree.
        */
        queue_remove(&queue, 0);
        reuse_freed_buff(&queue, top, key_length);
      }
    }
    top= (BUFFPEK *) queue_top(&queue);
    /* new top has been obtained; if old top is unique, apply the action */
    if (compare(compare_arg, old_key, top->key))
    {
      if (walk_action(old_key, 1, walk_action_arg))
        goto end;
    }
  }
  /*
    Applying walk_action to the tail of the last tree: this is safe because
    either we had only one tree in the beginning, either we work with the
    last tree in the queue.
  */
  do
  {
    do
    {
      if (walk_action(top->key, 1, walk_action_arg))
        goto end;
      top->key+= key_length;
    }
    while (--top->mem_count);
    bytes_read= read_to_buffer(file, top, key_length);
    if (bytes_read == (uint) (-1))
      goto end;
  }
  while (bytes_read);
  res= 0;
end:
  delete_queue(&queue);
  return res;
}


/*
  DESCRIPTION
    Walks consecutively through all unique elements:
    if all elements are in memory, then it simply invokes 'tree_walk', else
    all flushed trees are loaded to memory piece-by-piece, pieces are
    sorted, and action is called for each unique value.
    Note: so as merging resets file_ptrs state, this method can change
    internal Unique state to undefined: if you want to reuse Unique after
    walk() you must call reset() first!
  SYNOPSIS
    Unique:walk()
  All params are 'IN':
    action  function-visitor, typed in include/my_tree.h
            function is called for each unique element
    arg     argument for visitor, which is passed to it on each call
  RETURN VALUE
    0    OK
    <> 0 error
 */

bool Unique::walk(tree_walk_action action, void *walk_action_arg)
{
  int res;
  uchar *merge_buffer;

  if (elements == 0)                       /* the whole tree is in memory */
    return tree_walk(&tree, action, walk_action_arg, left_root_right);

  /* flush current tree to the file to have some memory for merge buffer */
  if (flush())
    return 1;
  if (flush_io_cache(&file) || reinit_io_cache(&file, READ_CACHE, 0L, 0, 0))
    return 1;
  if (!(merge_buffer= (uchar *) my_malloc((ulong) max_in_memory_size, MYF(0))))
    return 1;
  res= merge_walk(merge_buffer, (ulong) max_in_memory_size, size,
                  (BUFFPEK *) file_ptrs.buffer,
                  (BUFFPEK *) file_ptrs.buffer + file_ptrs.elements,
                  action, walk_action_arg,
                  tree.compare, tree.custom_arg, &file);
  my_free(merge_buffer);
  return res;
}

/*
  Modify the TABLE element so that when one calls init_records()
  the rows will be read in priority order.
*/

bool Unique::get(TABLE *table)
{
  SORTPARAM sort_param;
  table->sort.found_records=elements+tree.elements_in_tree;

  if (my_b_tell(&file) == 0)
  {
    /* Whole tree is in memory;  Don't use disk if you don't need to */
    if ((record_pointers=table->sort.record_pointers= (uchar*)
	 my_malloc(size * tree.elements_in_tree, MYF(0))))
    {
      (void) tree_walk(&tree, (tree_walk_action) unique_write_to_ptrs,
		       this, left_root_right);
      return 0;
    }
  }
  /* Not enough memory; Save the result to file && free memory used by tree */
  if (flush())
    return 1;

  IO_CACHE *outfile=table->sort.io_cache;
  BUFFPEK *file_ptr= (BUFFPEK*) file_ptrs.buffer;
  uint maxbuffer= file_ptrs.elements - 1;
  uchar *sort_buffer;
  my_off_t save_pos;
  bool error=1;

      /* Open cached file if it isn't open */
  outfile=table->sort.io_cache=(IO_CACHE*) my_malloc(sizeof(IO_CACHE),
                                MYF(MY_ZEROFILL));

  if (!outfile || (! my_b_inited(outfile) &&
      open_cached_file(outfile,mysql_tmpdir,TEMP_PREFIX,READ_RECORD_BUFFER,
		       MYF(MY_WME))))
    return 1;
  reinit_io_cache(outfile,WRITE_CACHE,0L,0,0);

  bzero((char*) &sort_param,sizeof(sort_param));
  sort_param.max_rows= elements;
  sort_param.sort_form=table;
  sort_param.rec_length= sort_param.sort_length= sort_param.ref_length=
    size;
  sort_param.keys= (uint) (max_in_memory_size / sort_param.sort_length);
  sort_param.not_killable=1;

  if (!(sort_buffer=(uchar*) my_malloc((sort_param.keys+1) *
				       sort_param.sort_length,
				       MYF(0))))
    return 1;
  sort_param.unique_buff= sort_buffer+(sort_param.keys*
				       sort_param.sort_length);

  sort_param.compare= (qsort2_cmp) buffpek_compare;
  sort_param.cmp_context.key_compare= tree.compare;
  sort_param.cmp_context.key_compare_arg= tree.custom_arg;

  /* Merge the buffers to one file, removing duplicates */
  if (merge_many_buff(&sort_param,sort_buffer,file_ptr,&maxbuffer,&file))
    goto err;
  if (flush_io_cache(&file) ||
      reinit_io_cache(&file,READ_CACHE,0L,0,0))
    goto err;
  if (merge_buffers(&sort_param, &file, outfile, sort_buffer, file_ptr,
		    file_ptr, file_ptr+maxbuffer,0))
    goto err;
  error=0;
err:
  my_free(sort_buffer);
  if (flush_io_cache(outfile))
    error=1;

  /* Setup io_cache for reading */
  save_pos=outfile->pos_in_file;
  if (reinit_io_cache(outfile,READ_CACHE,0L,0,0))
    error=1;
  outfile->end_of_file=save_pos;
  return error;
}