pgsql: Skip redundant anti-wraparound vacuums

From: Michael Paquier <michael(at)paquier(dot)xyz>
To: pgsql-committers(at)lists(dot)postgresql(dot)org
Subject: pgsql: Skip redundant anti-wraparound vacuums
Date: 2019-03-31 14:03:12
Message-ID: E1hAb3I-0004aD-Fh@gemulon.postgresql.org
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Skip redundant anti-wraparound vacuums

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

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/2aa6e331ead7f3ad080561495ad4bd3bc7cd8913

Modified Files
--------------
src/backend/access/heap/vacuumlazy.c | 24 ++++++++++++++++++++----
1 file changed, 20 insertions(+), 4 deletions(-)

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