From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Dawn Yu <boyyuxiao1987@gmail.com>
To: pgsql-admin@lists.postgresql.org
Subject: Re: A Question about FPW and WAL
Date: Mon, 03 Apr 2023 11:38:30 +0200
Message-ID: <942e247261151cddf5d57cf7797d6bf3c9b067a7.camel@cybertec.at> (raw)
In-Reply-To: <CALiuKDHL-5h4DWYKiCXpQHJ8UHEG7mKj38eJVGWeT=nf604bLQ@mail.gmail.com>
References: <CALiuKDHL-5h4DWYKiCXpQHJ8UHEG7mKj38eJVGWeT=nf604bLQ@mail.gmail.com>
On Mon, 2023-04-03 at 14:51 +0800, Dawn Yu wrote:
> Recently，we come up with a same problem，when the database make the checkpoint,
> the size of wal directory increase very fast and take one hundred percent disk
> usage,we found the problem of pg wal write amplification is very serious.
> By analyzing the wal log, in some scenarios, most of the space is wasted when
> maintaining the full page of the index. Has the community considered modifying
> this part of the relevant code to make the full page better,The setting of FPW
> function is divided into two parts, the full-page write of the data record and
> the full-page write of the index block, and the switch functions can be set
> separately.
> By default, index full-page write is disabled. If the index is broken, you can
> rebuild the index to solve it. Although the security of index data cannot be
> guaranteed, this setting can greatly reduce the problem of storage space explosion
> caused by wal write amplification.
I would feel funny about a parameter like that.
There are a couple of things you can do today:
- increase "max_wal_size" and "checkpoint_timeout" to get checkpoints less often
- activate "wal_compression", so that the FPW are compressed. Best is to use v15,
where you can use "lz4" or "zstd" compression, which are much faster.
Yours,
Laurenz Albe
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To: pgsql-admin@postgresql.org
Cc: laurenz.albe@cybertec.at, boyyuxiao1987@gmail.com, pgsql-admin@lists.postgresql.org
Subject: Re: A Question about FPW and WAL
In-Reply-To: <942e247261151cddf5d57cf7797d6bf3c9b067a7.camel@cybertec.at>
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