mirror of https://github.com/postgres/postgres
Move I/O before the index_update_stats() buffer lock region.
Commit a07e03fd8f
enlarged the work done
here under the pg_class heap buffer lock. Two preexisting actions are
best done before holding that lock. Both RelationGetNumberOfBlocks()
and visibilitymap_count() do I/O, and the latter might exclusive-lock a
visibility map buffer. Moving these reduces contention and risk of
undetected LWLock deadlock. Back-patch to v12, like that commit.
Discussion: https://postgr.es/m/20241031200139.b4@rfd.leadboat.com
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parent
2fa255ce9b
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@ -2806,6 +2806,9 @@ index_update_stats(Relation rel,
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bool hasindex,
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double reltuples)
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{
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bool update_stats;
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BlockNumber relpages;
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BlockNumber relallvisible;
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Oid relid = RelationGetRelid(rel);
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Relation pg_class;
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ScanKeyData key[1];
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@ -2814,6 +2817,42 @@ index_update_stats(Relation rel,
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Form_pg_class rd_rel;
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bool dirty;
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/*
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* As a special hack, if we are dealing with an empty table and the
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* existing reltuples is -1, we leave that alone. This ensures that
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* creating an index as part of CREATE TABLE doesn't cause the table to
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* prematurely look like it's been vacuumed. The rd_rel we modify may
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* differ from rel->rd_rel due to e.g. commit of concurrent GRANT, but the
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* commands that change reltuples take locks conflicting with ours. (Even
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* if a command changed reltuples under a weaker lock, this affects only
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* statistics for an empty table.)
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*/
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if (reltuples == 0 && rel->rd_rel->reltuples < 0)
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reltuples = -1;
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/*
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* Don't update statistics during binary upgrade, because the indexes are
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* created before the data is moved into place.
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*/
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update_stats = reltuples >= 0 && !IsBinaryUpgrade;
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/*
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* Finish I/O and visibility map buffer locks before
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* systable_inplace_update_begin() locks the pg_class buffer. The rd_rel
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* we modify may differ from rel->rd_rel due to e.g. commit of concurrent
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* GRANT, but no command changes a relkind from non-index to index. (Even
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* if one did, relallvisible doesn't break functionality.)
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*/
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if (update_stats)
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{
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relpages = RelationGetNumberOfBlocks(rel);
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if (rel->rd_rel->relkind != RELKIND_INDEX)
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visibilitymap_count(rel, &relallvisible, NULL);
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else /* don't bother for indexes */
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relallvisible = 0;
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}
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/*
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* We always update the pg_class row using a non-transactional,
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* overwrite-in-place update. There are several reasons for this:
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@ -2858,15 +2897,6 @@ index_update_stats(Relation rel,
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/* Should this be a more comprehensive test? */
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Assert(rd_rel->relkind != RELKIND_PARTITIONED_INDEX);
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/*
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* As a special hack, if we are dealing with an empty table and the
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* existing reltuples is -1, we leave that alone. This ensures that
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* creating an index as part of CREATE TABLE doesn't cause the table to
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* prematurely look like it's been vacuumed.
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*/
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if (reltuples == 0 && rd_rel->reltuples < 0)
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reltuples = -1;
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/* Apply required updates, if any, to copied tuple */
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dirty = false;
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@ -2876,20 +2906,8 @@ index_update_stats(Relation rel,
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dirty = true;
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}
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/*
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* Avoid updating statistics during binary upgrade, because the indexes
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* are created before the data is moved into place.
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*/
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if (reltuples >= 0 && !IsBinaryUpgrade)
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if (update_stats)
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{
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BlockNumber relpages = RelationGetNumberOfBlocks(rel);
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BlockNumber relallvisible;
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if (rd_rel->relkind != RELKIND_INDEX)
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visibilitymap_count(rel, &relallvisible, NULL);
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else /* don't bother for indexes */
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relallvisible = 0;
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if (rd_rel->relpages != (int32) relpages)
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{
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rd_rel->relpages = (int32) relpages;
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