From: Christoph Berg <myon@debian.org>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: Fujii Masao <masao.fujii@oss.nttdata.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: CHECKPOINT unlogged data
Date: Wed, 9 Jul 2025 23:21:59 +0200
Message-ID: <aG7ddyB-ESzJYAYp@msg.df7cb.de> (raw)
In-Reply-To: <aG7Cbf9dju1kkzGE@nathan>
References: <aEmIijETyhj9DsWG@msg.df7cb.de>
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<086ab9ad5a2c06eb16f6f4e50a04764ba6fafd1b.camel@cybertec.at>
<aFAsCyMj-mybBlv3@msg.df7cb.de>
<aFA10XSdJ9hPGfD1@nathan>
<aFA7ustE2APIMehs@msg.df7cb.de>
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<aG7Cbf9dju1kkzGE@nathan>
Re: Nathan Bossart
> Here is what I have staged for commit, which I'm planning to do on Friday.
> diff --git a/doc/src/sgml/ref/pg_basebackup.sgml b/doc/src/sgml/ref/pg_basebackup.sgml
> index 9659f76042c..9be752fc12b 100644
> --- a/doc/src/sgml/ref/pg_basebackup.sgml
> +++ b/doc/src/sgml/ref/pg_basebackup.sgml
> @@ -500,7 +500,7 @@ PostgreSQL documentation
> <term><option>--checkpoint={fast|spread}</option></term>
> <listitem>
> <para>
> - Sets checkpoint mode to fast (immediate) or spread (the default)
> + Sets checkpoint mode to fast or spread (the default)
> (see <xref linkend="backup-lowlevel-base-backup"/>).
This is somewhat hard to parse, perhaps combine the two ()() into one:
Sets checkpoint mode to fast or spread (the default is spread,
see <xref linkend="backup-lowlevel-base-backup"/>).
(patch 4)
> <para>
> - The <command>CHECKPOINT</command> command forces a fast
> + When <literal>MODE</literal> is set to <literal>FAST</literal>, which is the
> + default, the <command>CHECKPOINT</command> command forces a fast
> checkpoint when the command is issued, without waiting for a
> regular checkpoint scheduled by the system (controlled by the settings in
> <xref linkend="runtime-config-wal-checkpoints"/>).
Explaining what the option does when explicitly setting the default is
confusing. We should explain the opposite case instead:
The <command>CHECKPOINT</command> command issues a fast checkpoint
by default where writes run at full speed. When literal>MODE</literal>
is set to <literal>SPREAD</literal>, writes are instead limited
by the settings in <xref linkend="runtime-config-wal-checkpoints"/>.
(patch 5)
> <variablelist>
> + <varlistentry>
> + <term><literal>FLUSH_UNLOGGED</literal></term>
> + <listitem>
> + <para>
> + Normally, <command>CHECKPOINT</command> does not flush data files for
> + unlogged relations. This option, which is disabled by default, enables
> + flushing unlogged relations.
More precise:
Normally, <command>CHECKPOINT</command> does not flush dirty buffers of
unlogged relations. This option, which is disabled by default, enables
flushing unlogged relations to disk.
Christoph
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To: pgsql-hackers@postgresql.org
Cc: myon@debian.org, nathandbossart@gmail.com, laurenz.albe@cybertec.at, masao.fujii@oss.nttdata.com, andres@anarazel.de, pgsql-hackers@lists.postgresql.org
Subject: Re: CHECKPOINT unlogged data
In-Reply-To: <aG7ddyB-ESzJYAYp@msg.df7cb.de>
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