Date: Thu, 27 Sep 2018 18:05:40 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: martin.marques@gmail.com, pgsql-docs@lists.postgresql.org
Subject: Re: Incorrect description of autovacuum_vacuum_threshold and
 autovacuum_vacuum_scale_factor
Message-ID: <20180927210540.od23ee3aq4bpkbpj@alvherre.pgsql>
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On 2018-Sep-27, PG Doc comments form wrote:

> Page: https://www.postgresql.org/docs/10/static/runtime-config-autovacuum.html
> 
> This page lists the different autovacuum options. Describing
> autovacuum_vacuum_threshold and autovacuum_vacuum_scale_factor independently
> adds confusion unless you are also reading
> https://www.postgresql.org/docs/10/static/routine-vacuuming.html#AUTOVACUUM
> where we have a formula for the threshold and scale factor.

True.

> I suggest adding a reference for each one of the two parameters with a link
> to the "Routine Vacuuming" section.

I suggest adding "This number is added to the number coming from the
autovacuum_vacuum_scale_factor parameter for each table" just before the
"This parameter can only be set" phrase.  So we'd end up with this:

autovacuum_vacuum_threshold (integer)
Specifies the minimum number of updated or deleted tuples needed to trigger a VACUUM in any one table. The default is 50 tuples. This number is added to the number coming from the autovacuum_vacuum_scale_factor parameter for each table.  This parameter can only be set in the postgresql.conf file or on the server command line; but the setting can be overridden for individual tables by changing table storage parameters.

autovacuum_vacuum_scale_factor (floating point)
Specifies a fraction of the table size to add to autovacuum_vacuum_threshold when deciding whether to trigger a VACUUM. The default is 0.2 (20% of table size). This number is added to the autovacuum_vacuum_threshold parameter for each table.  This parameter can only be set in the postgresql.conf file or on the server command line; but the setting can be overridden for individual tables by changing table storage parameters.

Same for the analyze parameters.

I suppose we don't need any updates to the section of
https://www.postgresql.org/docs/10/static/sql-createtable.html that
explains the equivalent reloptions, since those ones are very succint
anyway.

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