database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-30 11:03:19 +03:00
Code Activity

pg_prewarm, a contrib module for prewarming relationd data.

Browse Source 
Patch by me.  Review by Álvaro Herrera, Amit Kapila, Jeff Janes,
Gurjeet Singh, and others.
This commit is contained in:
Robert Haas
2013-12-20 08:08:01 -05:00
parent 6eda3e9c27
commit c32afe53c2
9 changed files with 314 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

1
doc/src/sgml/contrib.sgml
View File

@ -128,6 +128,7 @@ CREATE EXTENSION <replaceable>module_name</> FROM unpackaged;
&pgbuffercache;
&pgcrypto;
&pgfreespacemap;
&pgprewarm;
&pgrowlocks;
&pgstatstatements;
&pgstattuple;

1
doc/src/sgml/filelist.sgml
View File

@ -126,6 +126,7 @@
<!ENTITY pgbuffercache SYSTEM "pgbuffercache.sgml">
<!ENTITY pgcrypto SYSTEM "pgcrypto.sgml">
<!ENTITY pgfreespacemap SYSTEM "pgfreespacemap.sgml">
<!ENTITY pgprewarm SYSTEM "pgprewarm.sgml">
<!ENTITY pgrowlocks SYSTEM "pgrowlocks.sgml">
<!ENTITY pgstandby SYSTEM "pgstandby.sgml">
<!ENTITY pgstatstatements SYSTEM "pgstatstatements.sgml">

68
doc/src/sgml/pgprewarm.sgml Normal file
View File

@ -0,0 +1,68 @@
<!-- doc/src/sgml/pgprewarm.sgml -->
<sect1 id="pgprewarm" xreflabel="pg_prewarm">
<title>pg_prewarm</title>
<indexterm zone="pgprewarm">
<primary>pg_prewarm</primary>
</indexterm>
<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.
</para>
<sect2>
<title>Functions</title>
<synopsis>
pg_prewarm(regclass, mode text default 'buffer', fork text default 'main',
first_block int8 default null,
last_block int8 default null) RETURNS int8
</synopsis>
<para>
The first argument is the relation to be prewarmed. The second argument
is the prewarming method to be used, as further discussed below; the third
is the relation fork to be prewarmed, usually <literal>main</literal>.
The fourth argument is the first block number to prewarm
(<literal>NULL</literal> is accepted as a synonym for zero). The fifth
argument is the last block number to prewarm (<literal>NULL</literal>
means prewarm through the last block in the relation). The return value
is the number of blocks prewarmed.
</para>
<para>
There are three available prewarming methods. <literal>prefetch</literal>
issues asynchronous prefetch requests to the operating system, if this is
supported, or throws an error otherwise. <literal>read</literal> reads
the requested range of blocks; unlike <literal>prefetch</literal>, this is
synchronous and supported on all platforms and builds, but may be slower.
<literal>buffer</literal> reads the requested range of blocks into the
database buffer cache.
</para>
<para>
Note that with any of these methods, attempting to prewarm more blocks than
can be cached &mdash; by the OS when using <literal>prefetch</literal> or
<literal>read</literal>, or by <productname>PostgreSQL</productname> when
using <literal>buffer</literal> &mdash; will likely result in lower-numbered
blocks being evicted as higher numbered blocks are read in. Prewarmed data
also enjoys no special protection from cache evictions, so it is possible
for other system activity may evict the newly prewarmed blocks shortly after
they are read; conversely, prewarming may also evict other data from cache.
For these reasons, prewarming is typically most useful at startup, when
caches are largely empty.
</para>
</sect2>
<sect2>
<title>Author</title>
<para>
Robert Haas <email>rhaas@postgresql.org</email>
</para>
</sect2>
</sect1>