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pg_prewarm: Add automatic prewarm feature.

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Periodically while the server is running, and at shutdown, write out a
list of blocks in shared buffers.  When the server reaches consistency
-- unfortunatey, we can't do it before that point without breaking
things -- reload those blocks into any still-unused shared buffers.

Mithun Cy and Robert Haas, reviewed and tested by Beena Emerson,
Amit Kapila, Jim Nasby, and Rafia Sabih.

Discussion: http://postgr.es/m/CAD__OugubOs1Vy7kgF6xTjmEqTR4CrGAv8w+ZbaY_+MZeitukw@mail.gmail.com
This commit is contained in:
Robert Haas
2017-08-21 14:43:00 -04:00
parent 66ed3829df
commit 79ccd7cbd5
11 changed files with 1035 additions and 4 deletions
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69
doc/src/sgml/pgprewarm.sgml
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@ -10,7 +10,13 @@
<para>
The <filename>pg_prewarm</filename> module provides a convenient way
to load relation data into either the operating system buffer cache
or the <productname>PostgreSQL</productname> buffer cache.
or the <productname>PostgreSQL</productname> buffer cache. Prewarming
can be performed manually using the <filename>pg_prewarm</> function,
or can be performed automatically by including <literal>pg_prewarm</> in
<xref linkend="guc-shared-preload-libraries">. In the latter case, the
system will run a background worker which periodically records the contents
of shared buffers in a file called <filename>autoprewarm.blocks</> and
will, using 2 background workers, reload those same blocks after a restart.
</para>
<sect2>
@ -55,6 +61,67 @@ pg_prewarm(regclass, mode text default 'buffer', fork text default 'main',
cache. For these reasons, prewarming is typically most useful at startup,
when caches are largely empty.
</para>
<synopsis>
autoprewarm_start_worker() RETURNS void
</synopsis>
<para>
Launch the main autoprewarm worker. This will normally happen
automatically, but is useful if automatic prewarm was not configured at
server startup time and you wish to start up the worker at a later time.
</para>
<synopsis>
autoprewarm_dump_now() RETURNS int8
</synopsis>
<para>
Update <filename>autoprewarm.blocks</> immediately. This may be useful
if the autoprewarm worker is not running but you anticipate running it
after the next restart. The return value is the number of records written
to <filename>autoprewarm.blocks</>.
</para>
</sect2>
<sect2>
<title>Configuration Parameters</title>
<variablelist>
<varlistentry>
<term>
<varname>pg_prewarm.autoprewarm</varname> (<type>boolean</type>)
<indexterm>
<primary><varname>pg_prewarm.autoprewarm</> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
Controls whether the server should run the autoprewarm worker. This is
on by default. This parameter can only be set at server start.
</para>
</listitem>
</varlistentry>
</variablelist>
<variablelist>
<varlistentry>
<term>
<varname>pg_prewarm.autoprewarm_interval</varname> (<type>int</type>)
<indexterm>
<primary><varname>pg_prewarm.autoprewarm_interval</> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
This is the interval between updates to <literal>autoprewarm.blocks</>.
The default is 300 seconds. If set to 0, the file will not be
dumped at regular intervals, but only when the server is shut down.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>