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| author | Thomas Munro <tmunro@postgresql.org> | 2025-03-19 11:40:56 +1300 |
|---|---|---|
| committer | Thomas Munro <tmunro@postgresql.org> | 2025-03-19 15:23:54 +1300 |
| commit | 10f6646847515b1ab02735c24b04abaf1996f65f (patch) | |
| tree | e49ca63aec12d99997f4fa91a6d4e3a11dbbe858 /doc/src | |
| parent | 17d8bba6dad12e14a7cafca9ef5eef21e577e9c3 (diff) | |
| download | postgresql-10f6646847515b1ab02735c24b04abaf1996f65f.tar.gz postgresql-10f6646847515b1ab02735c24b04abaf1996f65f.zip | |
Introduce io_max_combine_limit.
The existing io_combine_limit can be changed by users. The new
io_max_combine_limit is fixed at server startup time, and functions as a
silent clamp on the user setting. That in itself is probably quite
useful, but the primary motivation is:
aio_init.c allocates shared memory for all asynchronous IOs including
some per-block data, and we didn't want to waste memory you'd never used
by assuming they could be up to PG_IOV_MAX. This commit already halves
the size of 'AioHandleIov' and 'AioHandleData'. A follow-up commit can
now expand PG_IOV_MAX without affecting that.
Since our GUC system doesn't support dependencies or cross-checks
between GUCs, the user-settable one now assigns a "raw" value to
io_combine_limit_guc, and the lower of io_combine_limit_guc and
io_max_combine_limit is maintained in io_combine_limit.
Reviewed-by: Andres Freund <andres@anarazel.de> (earlier version)
Discussion: https://postgr.es/m/CA%2BhUKG%2B2T9p-%2BzM6Eeou-RAJjTML6eit1qn26f9twznX59qtCA%40mail.gmail.com
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/config.sgml | 23 |
1 files changed, 22 insertions, 1 deletions
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 9e9c02cde83..2988865b116 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -2625,6 +2625,24 @@ include_dir 'conf.d' </listitem> </varlistentry> + <varlistentry id="guc-io-max-combine-limit" xreflabel="io_max_combine_limit"> + <term><varname>io_max_combine_limit</varname> (<type>integer</type>) + <indexterm> + <primary><varname>io_max_combine_limit</varname> configuration parameter</primary> + </indexterm> + </term> + <listitem> + <para> + Controls the largest I/O size in operations that combine I/O, and silently + limits the user-settable parameter <varname>io_combine_limit</varname>. + This parameter can only be set in + the <filename>postgresql.conf</filename> file or on the server + command line. + The default is 128kB. + </para> + </listitem> + </varlistentry> + <varlistentry id="guc-io-combine-limit" xreflabel="io_combine_limit"> <term><varname>io_combine_limit</varname> (<type>integer</type>) <indexterm> @@ -2633,7 +2651,10 @@ include_dir 'conf.d' </term> <listitem> <para> - Controls the largest I/O size in operations that combine I/O. + Controls the largest I/O size in operations that combine I/O. If set + higher than the <varname>io_max_combine_limit</varname> parameter, the + lower value will silently be used instead, so both may need to be raised + to increase the I/O size. The default is 128kB. </para> </listitem> |