RE: reloption to prevent VACUUM from truncating empty pages at the end of relation

From: "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com>
To: 'Alvaro Herrera' <alvherre(at)2ndquadrant(dot)com>, 'Andres Freund' <andres(at)anarazel(dot)de>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Julien Rouhaud <rjuju123(at)gmail(dot)com>, David Steele <david(at)pgmasters(dot)net>, "Bossart, Nathan" <bossartn(at)amazon(dot)com>, "Andrew Dunstan" <andrew(dot)dunstan(at)2ndquadrant(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>, "Jamison, Kirk" <k(dot)jamison(at)jp(dot)fujitsu(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: RE: reloption to prevent VACUUM from truncating empty pages at the end of relation
Date: 2019-04-08 05:22:17
Message-ID: 0A3221C70F24FB45833433255569204D1FBF2EBA@G01JPEXMBYT05
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From: Alvaro Herrera [mailto:alvherre(at)2ndquadrant(dot)com]
> "vacuum_truncate" gets my vote too.


From: 'Andres Freund' [mailto:andres(at)anarazel(dot)de]
> Personally I think the name just needs some committer to make a
> call. This largely is going to be used after encountering too many
> cancellations in production, and researching the cause. Minor spelling
> differences don't seem to particularly matter here.

Absolutely. Thank you.

From: 'Andres Freund' [mailto:andres(at)anarazel(dot)de]
> I think it needs to be an autovac option. The production issue is that
> autovacuums constantly cancel queries on the standbys despite
> hot_standby_feedback if you have a workload that does frequent
> truncations. If there's no way to configure it in a way that autovacuum
> takes it into account, people will just disable autovacuum and rely
> entirely on manual scripts. That's what already happens - leading to a
> much bigger foot-gun than disabling truncation. FWIW, people already in
> production use the workaround to configuring snapshot_too_old as that,
> for undocumented reasons, disables trunctations. That's not better
> either.

Right. We don't want autovacuum to be considered as a criminal.

Takayuki Tsunakawa

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