Message-ID: <cda2f2e486d4889a23f7c1080433f462a93fc8e8.camel@cybertec.at>
Subject: Re: vacuum_freeze_min_age description validity
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: sanjaya.waruna@gmail.com, pgsql-docs@lists.postgresql.org
Date: Sat, 18 Sep 2021 00:08:03 +0200
In-Reply-To: <163186886974.4680.11795770889268302099@wrigleys.postgresql.org>
References: <163186886974.4680.11795770889268302099@wrigleys.postgresql.org>
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On Fri, 2021-09-17 at 08:54 +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/10/routine-vacuuming.html
> Description:
> 
> Hi All,
> I have a doubt about the vacuum_freeze_min_age explanation here;
> https://www.postgresql.org/docs/10/routine-vacuuming.html
> "vacuum_freeze_min_age controls how old an XID value has to be before rows
> bearing that XID will be frozen. Increasing this setting may avoid
> unnecessary work if the rows that would otherwise be frozen will soon be
> modified again, but decreasing this setting increases the number of
> transactions that can elapse before the table must be vacuumed again."
> 
> Shouldn't the "Increasing" and "decreasing" words there interchange the
> places? 
> Isn't decreasing value for vacuum_freeze_min_age causes vacuum to freeze
> tuples soon due to reduced age? So it reduces number of transactions that
> can elapse before the table must be vacuumed. 
> Please let me know if my understanding is incorrect. 

The documentation is correct.

If you increase the parameter, rows will be frozen later, so if the rows get
deleted before they would get frozen, you save the work of freezing them.

If you decrease the parameter, rows get frozen earlier, so the time until
anti-wraparound vacuum is necessary will increase.

Yours,
Laurenz Albe