From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Roberto Mello <roberto.mello@gmail.com>
Cc: PostgreSQL Developers <pgsql-hackers@lists.postgresql.org>
Subject: Re: doc: BRIN indexes and autosummarize
Date: Mon, 4 Jul 2022 17:20:11 +0200
Message-ID: <20220704152011.4rypgtgfu66rktkq@alvherre.pgsql> (raw)
In-Reply-To: <CAKz==bK_NoJytRyQfX8K-erCW3Ff7--oGYpiB8+ePVS7dRVW_A@mail.gmail.com>
On 2022-Jun-28, Roberto Mello wrote:
> Here's a patch to clarify the BRIN indexes documentation, particularly with
> regards to autosummarize, vacuum and autovacuum. It basically breaks
> down a big blob of a paragraph into multiple paragraphs for clarity,
> plus explicitly tells how summarization happens manually or
> automatically.
[Some of] these additions are wrong actually. It says that autovacuum
will not summarize new entries; but it does. If you just let the table
sit idle, any autovacuum run that cleans the table will also summarize
any ranges that need summarization.
What 'autosummarization=off' means is that the behavior to trigger an
immediate summarization of a range once it becomes full is not default.
This is very different.
As for the new <para></para>s that you added, I'd say they're
stylistically wrong. Each paragraph is supposed to be one fully
contained idea; what these tags do is split each idea across several
smaller paragraphs. This is likely subjective though.
> On this topic... I'm not familiar with with the internals of BRIN
> indexes and in backend/access/common/reloptions.c I see:
>
> {
> "autosummarize",
> "Enables automatic summarization on this BRIN index",
> RELOPT_KIND_BRIN,
> AccessExclusiveLock
> },
>
> Is the exclusive lock on the index why autosummarize is off by default?
No. The lock level mentioned here is what needs to be taken in order to
change the value of this option.
> What would be the downside (if any) of having autosummarize=on by default?
I'm not aware of any. Maybe we should turn it on by default.
--
Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: alvherre@alvh.no-ip.org, roberto.mello@gmail.com, pgsql-hackers@lists.postgresql.org
Subject: Re: doc: BRIN indexes and autosummarize
In-Reply-To: <20220704152011.4rypgtgfu66rktkq@alvherre.pgsql>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox