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Commita2e092e

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Don't MAXALIGN in the checks to decide whether a tuple is over TOAST's
threshold for tuple length. On 4-byte-MAXALIGN machines, the toast codecreates tuples that have t_len exactly TOAST_TUPLE_THRESHOLD ... but thisnumber is not itself maxaligned, so if heap_insert maxaligns t_len beforecomparing to TOAST_TUPLE_THRESHOLD, it'll uselessly recurse back totuptoaster.c, wasting cycles. (It turns out that this does not happen on8-byte-MAXALIGN machines, because for them the outer MAXALIGN in theTOAST_MAX_CHUNK_SIZE macro reduces TOAST_MAX_CHUNK_SIZE so that toast tupleswill be less than TOAST_TUPLE_THRESHOLD in size. That MAXALIGN is reallyincorrect, but we can't remove it now, see below.) There isn't any particularvalue in maxaligning before comparing to the thresholds, so just don't dothat, which saves a small number of cycles in itself.These numbers should be rejiggered to minimize wasted space on toast-relationpages, but we can't do that in the back branches because changingTOAST_MAX_CHUNK_SIZE would force an initdb (by changing the contents of toasttables). We can move the toast decision thresholds a bit, though, which iswhat this patch effectively does.Thanks to Pavan Deolasee for discovering the unintended recursion.Back-patch into 8.2, but not further, pending more testing. (HEAD is aboutto get a further patch modifying the thresholds, so it won't help muchfor testing this form of the patch.)
1 parent03d442c commita2e092e

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3 files changed

+31
-24
lines changed

3 files changed

+31
-24
lines changed

‎src/backend/access/heap/heapam.c

Lines changed: 6 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.225 2007/01/25 02:17:25 momjian Exp $
11+
* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.226 2007/02/04 20:00:37 tgl Exp $
1212
*
1313
*
1414
* INTERFACE ROUTINES
@@ -1418,8 +1418,7 @@ heap_insert(Relation relation, HeapTuple tup, CommandId cid,
14181418
* Note: below this point, heaptup is the data we actually intend to store
14191419
* into the relation; tup is the caller's original untoasted data.
14201420
*/
1421-
if (HeapTupleHasExternal(tup)||
1422-
(MAXALIGN(tup->t_len)>TOAST_TUPLE_THRESHOLD))
1421+
if (HeapTupleHasExternal(tup)||tup->t_len>TOAST_TUPLE_THRESHOLD)
14231422
heaptup=toast_insert_or_update(relation,tup,NULL,use_wal);
14241423
else
14251424
heaptup=tup;
@@ -2073,14 +2072,14 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
20732072
* We need to invoke the toaster if there are already any out-of-line
20742073
* toasted values present, or if the new tuple is over-threshold.
20752074
*/
2076-
newtupsize=MAXALIGN(newtup->t_len);
2077-
20782075
need_toast= (HeapTupleHasExternal(&oldtup)||
20792076
HeapTupleHasExternal(newtup)||
2080-
newtupsize>TOAST_TUPLE_THRESHOLD);
2077+
newtup->t_len>TOAST_TUPLE_THRESHOLD);
20812078

20822079
pagefree=PageGetFreeSpace((Page)dp);
20832080

2081+
newtupsize=MAXALIGN(newtup->t_len);
2082+
20842083
if (need_toast||newtupsize>pagefree)
20852084
{
20862085
oldtup.t_data->t_infomask &= ~(HEAP_XMAX_COMMITTED |
@@ -2100,7 +2099,7 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
21002099
*
21012100
* Note: below this point, heaptup is the data we actually intend to
21022101
* store into the relation; newtup is the caller's original untoasted
2103-
* data. (We always use WAL for toast table updates.)
2102+
* data.
21042103
*/
21052104
if (need_toast)
21062105
{

‎src/backend/access/heap/tuptoaster.c

Lines changed: 19 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/access/heap/tuptoaster.c,v 1.69 2007/01/25 02:17:26 momjian Exp $
11+
* $PostgreSQL: pgsql/src/backend/access/heap/tuptoaster.c,v 1.70 2007/02/04 20:00:37 tgl Exp $
1212
*
1313
*
1414
* INTERFACE ROUTINES
@@ -506,17 +506,23 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup, bool us
506506
*4: Store attributes with attstorage 'm' external
507507
* ----------
508508
*/
509+
510+
/* compute header overhead --- this should match heap_form_tuple() */
509511
maxDataLen= offsetof(HeapTupleHeaderData,t_bits);
510512
if (has_nulls)
511513
maxDataLen+=BITMAPLEN(numAttrs);
512-
maxDataLen=TOAST_TUPLE_TARGET-MAXALIGN(maxDataLen);
514+
if (newtup->t_data->t_infomask&HEAP_HASOID)
515+
maxDataLen+=sizeof(Oid);
516+
maxDataLen=MAXALIGN(maxDataLen);
517+
Assert(maxDataLen==newtup->t_data->t_hoff);
518+
/* now convert to a limit on the tuple data size */
519+
maxDataLen=TOAST_TUPLE_TARGET-maxDataLen;
513520

514521
/*
515522
* Look for attributes with attstorage 'x' to compress
516523
*/
517-
while (MAXALIGN(heap_compute_data_size(tupleDesc,
518-
toast_values,toast_isnull))>
519-
maxDataLen)
524+
while (heap_compute_data_size(tupleDesc,
525+
toast_values,toast_isnull)>maxDataLen)
520526
{
521527
intbiggest_attno=-1;
522528
int32biggest_size=MAXALIGN(sizeof(varattrib));
@@ -575,9 +581,9 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup, bool us
575581
* Second we look for attributes of attstorage 'x' or 'e' that are still
576582
* inline.
577583
*/
578-
while (MAXALIGN(heap_compute_data_size(tupleDesc,
579-
toast_values,toast_isnull))>
580-
maxDataLen&&rel->rd_rel->reltoastrelid!=InvalidOid)
584+
while (heap_compute_data_size(tupleDesc,
585+
toast_values,toast_isnull)>maxDataLen&&
586+
rel->rd_rel->reltoastrelid!=InvalidOid)
581587
{
582588
intbiggest_attno=-1;
583589
int32biggest_size=MAXALIGN(sizeof(varattrib));
@@ -627,9 +633,8 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup, bool us
627633
* Round 3 - this time we take attributes with storage 'm' into
628634
* compression
629635
*/
630-
while (MAXALIGN(heap_compute_data_size(tupleDesc,
631-
toast_values,toast_isnull))>
632-
maxDataLen)
636+
while (heap_compute_data_size(tupleDesc,
637+
toast_values,toast_isnull)>maxDataLen)
633638
{
634639
intbiggest_attno=-1;
635640
int32biggest_size=MAXALIGN(sizeof(varattrib));
@@ -687,9 +692,9 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup, bool us
687692
/*
688693
* Finally we store attributes of type 'm' external
689694
*/
690-
while (MAXALIGN(heap_compute_data_size(tupleDesc,
691-
toast_values,toast_isnull))>
692-
maxDataLen&&rel->rd_rel->reltoastrelid!=InvalidOid)
695+
while (heap_compute_data_size(tupleDesc,
696+
toast_values,toast_isnull)>maxDataLen&&
697+
rel->rd_rel->reltoastrelid!=InvalidOid)
693698
{
694699
intbiggest_attno=-1;
695700
int32biggest_size=MAXALIGN(sizeof(varattrib));

‎src/include/access/tuptoaster.h

Lines changed: 6 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -6,7 +6,7 @@
66
*
77
* Copyright (c) 2000-2007, PostgreSQL Global Development Group
88
*
9-
* $PostgreSQL: pgsql/src/include/access/tuptoaster.h,v 1.30 2007/01/25 02:17:26 momjian Exp $
9+
* $PostgreSQL: pgsql/src/include/access/tuptoaster.h,v 1.31 2007/02/04 20:00:37 tgl Exp $
1010
*
1111
*-------------------------------------------------------------------------
1212
*/
@@ -26,8 +26,11 @@
2626
/*
2727
* These symbols control toaster activation. If a tuple is larger than
2828
* TOAST_TUPLE_THRESHOLD, we will try to toast it down to no more than
29-
* TOAST_TUPLE_TARGET bytes. Both numbers include all tuple header and
30-
* alignment-padding overhead.
29+
* TOAST_TUPLE_TARGET bytes. Both numbers include all tuple header overhead
30+
* and between-fields alignment padding, but we do *not* consider any
31+
* end-of-tuple alignment padding; hence the values can be compared directly
32+
* to a tuple's t_len field. (Note that the symbol values are not
33+
* necessarily MAXALIGN multiples.)
3134
*
3235
* The numbers need not be the same, though they currently are.
3336
*/

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