From: | Richard Huxton <dev(at)archonet(dot)com> |
---|---|
To: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, gearond(at)cvc(dot)net |
Cc: | Dann Corbit <DCorbit(at)connx(dot)com>, Denis <denis(at)next2me(dot)com>, pgsql-performance(at)postgresql(dot)org, pgsql-general(at)postgresql(dot)org, pgsql-sql(at)postgresql(dot)org |
Subject: | Re: [PERFORM] Yet Another (Simple) Case of Index not used |
Date: | 2003-04-15 16:29:45 |
Message-ID: | 200304151729.45657.dev@archonet.com |
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Lists: | pgsql-general pgsql-performance pgsql-sql |
On Tuesday 15 Apr 2003 3:23 pm, Bruce Momjian wrote:
> Dennis Gearon wrote:
> > from mysql manual:
> > -------------------------------------------------------------
> > "COUNT(*) is optimized to return very quickly if the SELECT retrieves
> > from one table, no other columns are retrieved, and there is no WHERE
> > clause. For example:
> >
> > mysql> select COUNT(*) from student;"
> > -------------------------------------------------------------
> The cleanest way would probably be to create an aggregate cache system
> table, and to insert into it when someone does an unqualified aggregate,
> and to delete from it when someone modifies the table --- the MVCC tuple
> visibility rules are handled automatically. Queries can look in there
> to see if a visible cached value already exists. Of course, the big
> question is whether this would be a big win, and whether the cost of
> upkeep would justify it.
If the rule system could handle something like:
CREATE RULE quick_foo_count AS ON SELECT count(*) FROM foo
DO INSTEAD
SELECT quick_count FROM agg_cache WHERE tbl_name='foo';
The whole thing could be handled by user-space triggers/rules and still
invisible to the end-user.
--
Richard Huxton
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