Date: Wed, 27 Mar 2019 18:31:58 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Darafei =?utf-8?B?IktvbdGPcGEi?= Praliaskouski <me@komzpa.net>
Cc: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Berserk Autovacuum (let's save next Mandrill)
Message-ID: <20190327213158.GA21065@alvherre.pgsql>
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On 2019-Mar-27, Darafei "Komяpa" Praliaskouski wrote:

> Attached is sketch of small patch that fixes several edge cases with
> autovacuum. Long story short autovacuum never comes to append only tables,
> killing large productions.

Yeah, autovac is not coping with these scenarios (and probably others).
However, rather than taking your patch's idea verbatim, I think we
should have autovacuum use separate actions for those two (wildly
different) scenarios.  For example:

* certain tables would have some sort of partial scan that sets the
  visibility map.  There's no reason to invoke the whole vacuuming
  machinery.  I don't think this is limited to append-only tables, but
  rather those are just the ones that are affected the most.

* tables nearing wraparound danger should use the (yet to be committed)
  option to skip index cleaning, which makes the cleanup action faster.
  Again, no need for complete vacuuming.


-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services