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Skip redundant anti-wraparound vacuums

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An anti-wraparound vacuum has to be by definition aggressive as it needs
to work on all the pages of a relation.  However it can happen that due
to some concurrent activity an anti-wraparound vacuum is marked as
non-aggressive, which makes it redundant with a previous run, and
it is actually useless as an anti-wraparound vacuum should process all
the pages of a relation.  This commit makes such vacuums to be skipped.

An anti-wraparound vacuum not aggressive can be found easily by mixing
low values of autovacuum_freeze_max_age (to control anti-wraparound) and
autovacuum_freeze_table_age (to control the aggressiveness).

28a8fa9 has added some extra logging printing all the possible
combinations of anti-wraparound and aggressive vacuums, which now gets
simplified as an anti-wraparound vacuum also non-aggressive gets
skipped.

Per discussion mainly between Andrew Dunstan, Robert Haas, Álvaro
Herrera, Kyotaro Horiguchi, Masahiko Sawada, and myself.

Author: Kyotaro Horiguchi, Michael Paquier
Reviewed-by: Andrew Dunstan, Álvaro Herrera
Discussion: https://postgr.es/m/20180914153554.562muwr3uwujno75@alvherre.pgsql
This commit is contained in:
Michael Paquier 2019-03-31 22:59:12 +09:00
parent 47b3c26642
commit 2aa6e331ea
1 changed files with 20 additions and 4 deletions
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22
src/backend/access/heap/vacuumlazy.c
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@ -248,6 +248,23 @@ heap_vacuum_rel(Relation onerel, VacuumParams *params,
if (params->options & VACOPT_DISABLE_PAGE_SKIPPING)
aggressive = true;
/*
* Normally the relfrozenxid for an anti-wraparound vacuum will be old
* enough to force an aggressive vacuum. However, a concurrent vacuum
* might have already done this work that the relfrozenxid in relcache has
* been updated. If that happens this vacuum is redundant, so skip it.
*/
if (params->is_wraparound && !aggressive)
{
ereport(DEBUG1,
(errmsg("skipping redundant vacuum to prevent wraparound of table \"%s.%s.%s\"",
get_database_name(MyDatabaseId),
get_namespace_name(RelationGetNamespace(onerel)),
RelationGetRelationName(onerel))));
pgstat_progress_end_command();
return;
}
vacrelstats = (LVRelStats *) palloc0(sizeof(LVRelStats));
vacrelstats->old_rel_pages = onerel->rd_rel->relpages;
@ -375,10 +392,9 @@ heap_vacuum_rel(Relation onerel, VacuumParams *params,
initStringInfo(&buf);
if (params->is_wraparound)
{
if (aggressive)
/* an anti-wraparound vacuum has to be aggressive */
Assert(aggressive);
msgfmt = _("automatic aggressive vacuum to prevent wraparound of table \"%s.%s.%s\": index scans: %d\n");
else
msgfmt = _("automatic vacuum to prevent wraparound of table \"%s.%s.%s\": index scans: %d\n");
}
else
{