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Date: Tue, 14 Oct 2003 12:48:06 -0400 (EDT)
From: Wei Weng <wweng@kencast.com>
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To: Christopher Kings-Lynne <chriskl@familyhealth.com.au>
Cc: Chris Faulkner <chrisf@oramap.com>,
	Pgsql-Performance <pgsql-performance@postgresql.org>,
	Pgsql-Sql <pgsql-sql@postgresql.org>
Subject: Re: [SQL] sql performance and cache
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On Sat, 11 Oct 2003, Christopher Kings-Lynne wrote:

> 
> > I have two very similar queries which I need to execute. They both have
> > exactly the same from / where conditions. When I execute the first, it takes
> > about 16 seconds. The second is executed almost immediately after, it takes
> > 13 seconds. In short, I'd like to know why the query result isn't being
> > cached and any ideas on how to improve the execution.
> 
> <snip>
> 
> > OK - so I could execute the query once, and get the maximum size of the
> > array and the result set in one. I know what I am doing is less than optimal
> > but I had expected the query results to be cached. So the second execution
> > would be very quick. So why aren't they ? I have increased my cache size -
> > shared_buffers is 2000 and I have doubled the default max_fsm... settings
> > (although I am not sure what they do). sort_mem is 8192.
> 
> PostgreSQL does not have, and has never had a query cache - so nothing 
> you do is going to make that second query faster.
> 
> Perhaps you are confusing it with the MySQL query cache?
> 
> Chris
> 
Is there plan on developing one (query cache)?

Thanks

Wei