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Document how *_blks_read statistics columns are computed.

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Bruce Momjian 2009-04-10 03:13:36 +00:00
parent 4c9c0b85fb
commit 51781146a8
1 changed files with 4 additions and 3 deletions
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doc/src/sgml/monitoring.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/monitoring.sgml,v 1.67 2009/04/09 22:32:02 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/monitoring.sgml,v 1.68 2009/04/10 03:13:36 momjian Exp $ -->
<chapter id="monitoring">
<title>Monitoring Database Activity</title>
@ -927,8 +927,9 @@ postgres: <replaceable>user</> <replaceable>database</> <replaceable>host</> <re
<function>pg_stat_get_blocks_fetched</function> minus
<function>pg_stat_get_blocks_hit</function> gives the number of kernel
<function>read()</> calls issued for the table, index, or
database; but the actual number of physical reads is usually
lower due to kernel-level buffering.
database; the number of actual physical reads is usually
lower due to kernel-level buffering. The <literal>*_blks_read</>
statistics columns uses this subtraction, i.e. fetched minus hit.
</para>
</note>