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Add prefetching support on macOS

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macOS doesn't have posix_fadvise(), but fcntl() with the F_RDADVISE
command does the same thing.

Some related documentation has been generalized to not mention
posix_advise() specifically anymore.

Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/0827edec-1317-4917-a186-035eb1e3241d%40eisentraut.org
This commit is contained in:
Peter Eisentraut
2024-08-28 07:26:48 +02:00
parent 2e6a8047f0
commit 6654bb9204
6 changed files with 54 additions and 35 deletions
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14
doc/src/sgml/config.sgml
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@ -2679,11 +2679,9 @@ include_dir 'conf.d'
</para>
<para>
Asynchronous I/O depends on an effective <function>posix_fadvise</function>
function, which some operating systems lack. If the function is not
present then setting this parameter to anything but zero will result
in an error. On some operating systems (e.g., Solaris), the function
is present but does not actually do anything.
Asynchronous I/O requires that the operating system supports issuing
read-ahead advice. If there is no operating system support then
setting this parameter to anything but zero will result in an error.
</para>
<para>
@ -3852,10 +3850,8 @@ include_dir 'conf.d'
<literal>off</literal>, <literal>on</literal> and
<literal>try</literal> (the default). The setting
<literal>try</literal> enables
prefetching only if the operating system provides the
<function>posix_fadvise</function> function, which is currently used
to implement prefetching. Note that some operating systems provide the
function, but it doesn't do anything.
prefetching only if the operating system provides support for issuing
read-ahead advice.
</para>
<para>
Prefetching blocks that will soon be needed can reduce I/O wait times

4
doc/src/sgml/wal.sgml
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@ -841,8 +841,8 @@
The <xref linkend="guc-maintenance-io-concurrency"/> and
<xref linkend="guc-wal-decode-buffer-size"/> settings limit prefetching
concurrency and distance, respectively. By default, it is set to
<literal>try</literal>, which enables the feature on systems where
<function>posix_fadvise</function> is available.
<literal>try</literal>, which enables the feature on systems that support
issuing read-ahead advice.
</para>
</sect1>