From: | "Jim C(dot) Nasby" <jim(at)nasby(dot)net> |
---|---|
To: | Josh Berkus <josh(at)agliodbs(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, 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: | 2003-04-22 08:23:39 |
Message-ID: | 20030422032339.A37876@flake.decibel.org |
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Lists: | pgsql-general pgsql-performance pgsql-sql |
On Sat, Apr 19, 2003 at 12:03:18PM -0700, Josh Berkus wrote:
> Kevin, Tom:
>
> > (The cheapness can be disputed as well, since it creates a single point
> > of contention for all inserts and deletes on the table. But that's a
> > different topic.)
>
> Actually, this was the problem with the trigger method of maintaining COUNT
> information in PostgreSQL. The statistics table itself becomes a
> significant souce of delay, since if a table_A gets 10,000 rows updated than
> table_count_A must necessarily be updated 10,000 times ... creating a lot of
> dead tuples and severely attenuating the table on disk until the next vacuum
> ... resulting in Update #10,000 to table_count_A taking 100+ times as long as
> Update #1 does, due to the required random seek time on disk.
Once statement level triggers are implimented, the performance would
probably be fine, assuming your update was a single statement.
--
Jim C. Nasby (aka Decibel!) jim(at)nasby(dot)net
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