From: Tom Lane <tgl@sss.pgh.pa.us>
To: Greg Smith <gsmith@gregsmith.com>
Cc: Alvaro Herrera <alvherre@commandprompt.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: I/O on select count(*)
Date: Thu, 15 May 2008 03:07:09 -0400
Message-ID: <28388.1210835229@sss.pgh.pa.us> (raw)
In-Reply-To: <Pine.GSO.4.64.0805142211300.5617@westnet.com>
References: <920841.71690.qm@web44808.mail.sp1.yahoo.com>
<482B1D5F.EE98.0025.0@wicourts.gov>
<Pine.GSO.4.64.0805142133250.27290@westnet.com>
<20080515020553.GN9838@alvh.no-ip.org>
<Pine.GSO.4.64.0805142211300.5617@westnet.com>
Greg Smith <gsmith@gregsmith.com> writes:
> ... To put that another way: if I've run a manual vacuum, is it true
> that it will have updated all the hint bits to XMIN_COMMITTED for all the
> tuples that were all done when the vacuum started?
Any examination whatsoever of a tuple --- whether by vacuum or any
ordinary DML operation --- will update its hint bits to match the
commit/abort status of the inserting/deleting transaction(s) as of
the instant of the examination. Your statement above is true but
is weaker than reality.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, gsmith@gregsmith.com, alvherre@commandprompt.com
Subject: Re: I/O on select count(*)
In-Reply-To: <28388.1210835229@sss.pgh.pa.us>
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