Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
> > http://developer.postgresql.org/pgdocs/postgres/monitoring-stats.html
> > says: "Note: blocks_fetched minus blocks_hit gives the number of
> > kernel read() calls issued for the table, index, or database; but the
> > actual number of physical reads is usually lower due to kernel-level
> > buffering." This seems to imply that anything that increases
> > blocks_hit should also increase blocks_fetched, but that doesn't seem
> > to match the actual behavior.
>
> > rhaas=# select heap_blks_read, heap_blks_hit from pg_statio_user_tables;
>
> It's talking about the underlying pg_stat_get_db_blocks_fetched()
> function, not heap_blks_read which is just a view field defined as
>
> pg_stat_get_blocks_fetched(C.oid) -
> pg_stat_get_blocks_hit(C.oid) AS heap_blks_read,
>
> Probably that sentence ought to spell out the full function name
> instead of abbreviating.
Done.
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
Index: doc/src/sgml/monitoring.sgml
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diff -c -c -r1.66 monitoring.sgml
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<note>
<para>
! <function>blocks_fetched</function> minus
! <function>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.
--- 924,931 ----
<note>
<para>
! <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.
