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Re: understanding pg_stat* numbers

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Oleg Bartunov <oleg(at)sai(dot)msu(dot)su>
Cc: Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: understanding pg_stat* numbers
Date: 2005-03-26 21:05:04
Message-ID: 18156.1111871104@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Oleg Bartunov <oleg(at)sai(dot)msu(dot)su> writes:
> I'm looking for blocks *actually* read from disk, since IO is the most 
> important factor.

Well, you won't find that out from Postgres, since it has no idea
whether a read() request was satisfied from kernel disk cache or had
to actually go to disk.

You could turn on log_statement_stats to get some possibly-more-reliable
numbers from the kernel via getrusage(), but this will only tell you
about totals across the whole backend process, not per-relation ...

			regards, tom lane

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