To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Kevin Brown <kevin@sysexperts.com>,
	pgsql-performance@postgresql.org
Subject: Re: [SQL] Yet Another (Simple) Case of Index not used
References: <EKEBJNAJDPKJBDFGJNIJAENMDBAA.denis@next2me.com>
	<200304090918.45275.josh@agliodbs.com> <20030419130146.GI1847@filer>
	<21955.1050767928@sss.pgh.pa.us> <20030420011336.GJ1847@filer>
	<24735.1050809664@sss.pgh.pa.us>
In-Reply-To: <24735.1050809664@sss.pgh.pa.us>
From: Greg Stark <gsstark@mit.edu>
Organization: The Emacs Conspiracy; member since 1992
Date: 23 Apr 2003 12:32:09 -0400
Message-ID: <87adeh2n06.fsf@stark.dyndns.tv>
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Tom Lane <tgl@sss.pgh.pa.us> writes:

> AFAICS, central-counter techniques could only work in an MVCC system
> if each transaction copies every counter in the system at each snapshot
> freeze point, in case it finds itself needing that counter value later
> on.  This is a huge amount of mostly-useless overhead, and it makes the
> problem of lock contention for access to the counters several orders of
> magnitude worse than you'd first think.

Well, one option would be to do it in a lazy way. If you do an update on a
table with cached aggregate data just throw the data out. This way you get to
cache data on infrequently updated tables and get only a very small penalty on
frequently updated tables.

--
greg