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Commitdea7d54

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If a field is incompressible ('compressed' data is actually larger than
source, due to addition of header overhead), store it as plain datarather than pseudo-compressed data. This saves a few microseconds whenreading it out, but much more importantly guarantees that the toasterwon't actually expand tuples that contain incompressible data. That'sessential to avoid 'Tuple too big' failures with large objects.
1 parent62bc33d commitdea7d54

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1 file changed

+65
-29
lines changed

1 file changed

+65
-29
lines changed

‎src/backend/access/heap/tuptoaster.c‎

Lines changed: 65 additions & 29 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/access/heap/tuptoaster.c,v 1.12 2000/08/04 04:16:07 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/access/heap/tuptoaster.c,v 1.13 2000/10/23 23:42:04 tgl Exp $
1212
*
1313
*
1414
* INTERFACE ROUTINES
@@ -247,6 +247,11 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup)
247247

248248
/* ----------
249249
* Then collect information about the values given
250+
*
251+
* NOTE: toast_action[i] can have these values:
252+
*' 'default handling
253+
*'p'already processed --- don't touch it
254+
*'x'incompressible, but OK to move off
250255
* ----------
251256
*/
252257
memset(toast_action,' ',numAttrs*sizeof(char));
@@ -397,14 +402,15 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup)
397402
intbiggest_attno=-1;
398403
int32biggest_size=MAXALIGN(sizeof(varattrib));
399404
Datumold_value;
405+
Datumnew_value;
400406

401407
/* ----------
402408
* Search for the biggest yet uncompressed internal attribute
403409
* ----------
404410
*/
405411
for (i=0;i<numAttrs;i++)
406412
{
407-
if (toast_action[i]=='p')
413+
if (toast_action[i]!='')
408414
continue;
409415
if (VARATT_IS_EXTENDED(toast_values[i]))
410416
continue;
@@ -421,20 +427,29 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup)
421427
break;
422428

423429
/* ----------
424-
*Compress it inline
430+
*Attempt to compress it inline
425431
* ----------
426432
*/
427433
i=biggest_attno;
428434
old_value=toast_values[i];
435+
new_value=toast_compress_datum(old_value);
429436

430-
toast_values[i]=toast_compress_datum(toast_values[i]);
431-
if (toast_free[i])
432-
pfree(DatumGetPointer(old_value));
433-
toast_free[i]= true;
434-
toast_sizes[i]=VARATT_SIZE(toast_values[i]);
435-
436-
need_change= true;
437-
need_free= true;
437+
if (DatumGetPointer(new_value)!=NULL)
438+
{
439+
/* successful compression */
440+
if (toast_free[i])
441+
pfree(DatumGetPointer(old_value));
442+
toast_values[i]=new_value;
443+
toast_free[i]= true;
444+
toast_sizes[i]=VARATT_SIZE(toast_values[i]);
445+
need_change= true;
446+
need_free= true;
447+
}
448+
else
449+
{
450+
/* incompressible data, ignore on subsequent compression passes */
451+
toast_action[i]='x';
452+
}
438453
}
439454

440455
/* ----------
@@ -504,14 +519,15 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup)
504519
intbiggest_attno=-1;
505520
int32biggest_size=MAXALIGN(sizeof(varattrib));
506521
Datumold_value;
522+
Datumnew_value;
507523

508524
/* ----------
509525
* Search for the biggest yet uncompressed internal attribute
510526
* ----------
511527
*/
512528
for (i=0;i<numAttrs;i++)
513529
{
514-
if (toast_action[i]=='p')
530+
if (toast_action[i]!='')
515531
continue;
516532
if (VARATT_IS_EXTENDED(toast_values[i]))
517533
continue;
@@ -528,22 +544,29 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup)
528544
break;
529545

530546
/* ----------
531-
*Compress it inline
547+
*Attempt to compress it inline
532548
* ----------
533549
*/
534550
i=biggest_attno;
535551
old_value=toast_values[i];
552+
new_value=toast_compress_datum(old_value);
536553

537-
toast_values[i]=toast_compress_datum(toast_values[i]);
538-
539-
if (toast_free[i])
540-
pfree(DatumGetPointer(old_value));
541-
542-
toast_free[i]= true;
543-
toast_sizes[i]=VARATT_SIZE(toast_values[i]);
544-
545-
need_change= true;
546-
need_free= true;
554+
if (DatumGetPointer(new_value)!=NULL)
555+
{
556+
/* successful compression */
557+
if (toast_free[i])
558+
pfree(DatumGetPointer(old_value));
559+
toast_values[i]=new_value;
560+
toast_free[i]= true;
561+
toast_sizes[i]=VARATT_SIZE(toast_values[i]);
562+
need_change= true;
563+
need_free= true;
564+
}
565+
else
566+
{
567+
/* incompressible data, ignore on subsequent compression passes */
568+
toast_action[i]='x';
569+
}
547570
}
548571

549572
/* ----------
@@ -690,20 +713,33 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup)
690713
* toast_compress_datum -
691714
*
692715
*Create a compressed version of a varlena datum
716+
*
717+
*If we fail (ie, compressed result is actually bigger than original)
718+
*then return NULL. We must not use compressed data if it'd expand
719+
*the tuple!
693720
* ----------
694721
*/
695722
staticDatum
696723
toast_compress_datum(Datumvalue)
697724
{
698725
varattrib*tmp;
699726

700-
tmp= (varattrib*)palloc(sizeof(PGLZ_Header)+VARATT_SIZE(value));
727+
tmp= (varattrib*)palloc(sizeof(PGLZ_Header)+VARATT_SIZE(value));
701728
pglz_compress(VARATT_DATA(value),VARATT_SIZE(value)-VARHDRSZ,
702-
(PGLZ_Header*)tmp,
703-
PGLZ_strategy_default);
704-
VARATT_SIZEP(tmp) |=VARATT_FLAG_COMPRESSED;
705-
706-
returnPointerGetDatum(tmp);
729+
(PGLZ_Header*)tmp,
730+
PGLZ_strategy_default);
731+
if (VARATT_SIZE(tmp)<VARATT_SIZE(value))
732+
{
733+
/* successful compression */
734+
VARATT_SIZEP(tmp) |=VARATT_FLAG_COMPRESSED;
735+
returnPointerGetDatum(tmp);
736+
}
737+
else
738+
{
739+
/* incompressible data */
740+
pfree(tmp);
741+
returnPointerGetDatum(NULL);
742+
}
707743
}
708744

709745

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