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Re: [SQL] Yet Another (Simple) Case of Index not used

From: Greg Stark <gsstark(at)mit(dot)edu>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Kevin Brown <kevin(at)sysexperts(dot)com>,pgsql-performance(at)postgresql(dot)org
Subject: Re: [SQL] Yet Another (Simple) Case of Index not used
Date: 2003-04-23 16:32:09
Message-ID: 87adeh2n06.fsf@stark.dyndns.tv (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-performancepgsql-sql
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)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


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