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Re: So, is COUNT(*) fast now?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: So, is COUNT(*) fast now?
Date: 2011-10-28 18:48:54
Message-ID: 27592.1319827734@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> I also tried changing the BufferIsValid() tests in
> visibilitymap_test() to use BufferIsInvalid() instead, with the sense
> of the tests reversed (see attached vismap-test-invalid.patch).  Since
> BufferIsInvalid() just checks for InvalidBuffer instead of also doing
> the sanity checks, it's significantly cheaper.  This also reduced the
> time to about 330 ms, so seems clearly worth doing.

Hmm.  I wonder whether it wouldn't be better to get rid of the range
checks in BufferIsValid, or better convert them into Asserts.  It seems
less than intuitive that BufferIsValid and BufferIsInvalid aren't simple
inverses.

			regards, tom lane

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