Message-ID: <41A46A2E.8030606@archonet.com>
Date: Wed, 24 Nov 2004 11:02:06 +0000
From: Richard Huxton <dev@archonet.com>
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To: BBI Edwin Punzalan <edwin@bluebamboo.ph>
Cc: pgsql-performance@postgresql.org
Subject: Re: FW: FW: Index usage
References: <000701c4d211$f039bfd0$b400a8c0@bluebamboo.ph>
In-Reply-To: <000701c4d211$f039bfd0$b400a8c0@bluebamboo.ph>
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BBI Edwin Punzalan wrote:
> Hi.
> 
> 1) chatlogs rows increases every now and then (its in a live environment)
> and currently have 538,696 rows

OK, so as a rule of thumb I'd say if you were fetching less than 5000 
rows it's bound to use an index. If more than 50,000 always use a 
seqscan, otherwise it'll depend on configuration settings. It looks like 
you settings are suggesting the cost of an index-scan vs seq-scan are 
greater than they are.

> 2) this is the only problem we experienced.  So far, all our other indexes
> are being used correctly.

Good.

> 3) I don't remember tuning any post-installation configuration of our
> postgreSQL except setting fsync to false.

So long as you know why this can cause data loss. It won't affect this 
problem.

Read that performance article I linked to in the last message, it's 
written by two people who know what they're talking about. The standard 
configuration settings are designed to work on any machine, not provide 
good performance. Work through the basics there and we can look at 
random_page_cost etc. if it's still causing you problems.

-- 
   Richard Huxton
   Archonet Ltd