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Commit6b01cac

Browse files
committed
Move I/O before the index_update_stats() buffer lock region.
Commita07e03f enlarged the work donehere under the pg_class heap buffer lock. Two preexisting actions arebest done before holding that lock. Both RelationGetNumberOfBlocks()and visibilitymap_count() do I/O, and the latter might exclusive-lock avisibility map buffer. Moving these reduces contention and risk ofundetected LWLock deadlock. Back-patch to v12, like that commit.Discussion:https://postgr.es/m/20241031200139.b4@rfd.leadboat.com
1 parentfe8091c commit6b01cac

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+36
-9
lines changed

1 file changed

+36
-9
lines changed

‎src/backend/catalog/index.c

Lines changed: 36 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -2788,6 +2788,9 @@ index_update_stats(Relation rel,
27882788
boolhasindex,
27892789
doublereltuples)
27902790
{
2791+
boolupdate_stats;
2792+
BlockNumberrelpages;
2793+
BlockNumberrelallvisible;
27912794
Oidrelid=RelationGetRelid(rel);
27922795
Relationpg_class;
27932796
ScanKeyDatakey[1];
@@ -2796,6 +2799,38 @@ index_update_stats(Relation rel,
27962799
Form_pg_classrd_rel;
27972800
booldirty;
27982801

2802+
/*
2803+
* As a special hack, if we are dealing with an empty table and the
2804+
* existing reltuples is -1, we leave that alone. This ensures that
2805+
* creating an index as part of CREATE TABLE doesn't cause the table to
2806+
* prematurely look like it's been vacuumed. The rd_rel we modify may
2807+
* differ from rel->rd_rel due to e.g. commit of concurrent GRANT, but the
2808+
* commands that change reltuples take locks conflicting with ours. (Even
2809+
* if a command changed reltuples under a weaker lock, this affects only
2810+
* statistics for an empty table.)
2811+
*/
2812+
if (reltuples==0&&rel->rd_rel->reltuples<0)
2813+
reltuples=-1;
2814+
2815+
update_stats=reltuples >=0;
2816+
2817+
/*
2818+
* Finish I/O and visibility map buffer locks before
2819+
* systable_inplace_update_begin() locks the pg_class buffer. The rd_rel
2820+
* we modify may differ from rel->rd_rel due to e.g. commit of concurrent
2821+
* GRANT, but no command changes a relkind from non-index to index. (Even
2822+
* if one did, relallvisible doesn't break functionality.)
2823+
*/
2824+
if (update_stats)
2825+
{
2826+
relpages=RelationGetNumberOfBlocks(rel);
2827+
2828+
if (rel->rd_rel->relkind!=RELKIND_INDEX)
2829+
visibilitymap_count(rel,&relallvisible,NULL);
2830+
else/* don't bother for indexes */
2831+
relallvisible=0;
2832+
}
2833+
27992834
/*
28002835
* We always update the pg_class row using a non-transactional,
28012836
* overwrite-in-place update. There are several reasons for this:
@@ -2849,16 +2884,8 @@ index_update_stats(Relation rel,
28492884
dirty= true;
28502885
}
28512886

2852-
if (reltuples >=0)
2887+
if (update_stats)
28532888
{
2854-
BlockNumberrelpages=RelationGetNumberOfBlocks(rel);
2855-
BlockNumberrelallvisible;
2856-
2857-
if (rd_rel->relkind!=RELKIND_INDEX)
2858-
visibilitymap_count(rel,&relallvisible,NULL);
2859-
else/* don't bother for indexes */
2860-
relallvisible=0;
2861-
28622889
if (rd_rel->relpages!= (int32)relpages)
28632890
{
28642891
rd_rel->relpages= (int32)relpages;

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