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Commit2aa6e33

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Skip redundant anti-wraparound vacuums
An anti-wraparound vacuum has to be by definition aggressive as it needsto work on all the pages of a relation. However it can happen that dueto some concurrent activity an anti-wraparound vacuum is marked asnon-aggressive, which makes it redundant with a previous run, andit is actually useless as an anti-wraparound vacuum should process allthe pages of a relation. This commit makes such vacuums to be skipped.An anti-wraparound vacuum not aggressive can be found easily by mixinglow values of autovacuum_freeze_max_age (to control anti-wraparound) andautovacuum_freeze_table_age (to control the aggressiveness).28a8fa9 has added some extra logging printing all the possiblecombinations of anti-wraparound and aggressive vacuums, which now getssimplified as an anti-wraparound vacuum also non-aggressive getsskipped.Per discussion mainly between Andrew Dunstan, Robert Haas, ÁlvaroHerrera, Kyotaro Horiguchi, Masahiko Sawada, and myself.Author: Kyotaro Horiguchi, Michael PaquierReviewed-by: Andrew Dunstan, Álvaro HerreraDiscussion:https://postgr.es/m/20180914153554.562muwr3uwujno75@alvherre.pgsql
1 parent47b3c26 commit2aa6e33

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1 file changed

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1 file changed

+20
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‎src/backend/access/heap/vacuumlazy.c

Lines changed: 20 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -248,6 +248,23 @@ heap_vacuum_rel(Relation onerel, VacuumParams *params,
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if (params->options&VACOPT_DISABLE_PAGE_SKIPPING)
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aggressive= true;
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/*
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* Normally the relfrozenxid for an anti-wraparound vacuum will be old
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* enough to force an aggressive vacuum. However, a concurrent vacuum
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* might have already done this work that the relfrozenxid in relcache has
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* been updated. If that happens this vacuum is redundant, so skip it.
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*/
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if (params->is_wraparound&& !aggressive)
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{
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ereport(DEBUG1,
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(errmsg("skipping redundant vacuum to prevent wraparound of table \"%s.%s.%s\"",
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get_database_name(MyDatabaseId),
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get_namespace_name(RelationGetNamespace(onerel)),
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RelationGetRelationName(onerel))));
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pgstat_progress_end_command();
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return;
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}
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vacrelstats= (LVRelStats*)palloc0(sizeof(LVRelStats));
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vacrelstats->old_rel_pages=onerel->rd_rel->relpages;
@@ -375,10 +392,9 @@ heap_vacuum_rel(Relation onerel, VacuumParams *params,
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initStringInfo(&buf);
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if (params->is_wraparound)
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{
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if (aggressive)
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msgfmt=_("automatic aggressive vacuum to prevent wraparound of table \"%s.%s.%s\": index scans: %d\n");
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else
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msgfmt=_("automatic vacuum to prevent wraparound of table \"%s.%s.%s\": index scans: %d\n");
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/* an anti-wraparound vacuum has to be aggressive */
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Assert(aggressive);
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msgfmt=_("automatic aggressive vacuum to prevent wraparound of table \"%s.%s.%s\": index scans: %d\n");
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}
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else
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{

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