Message-ID: <45BAFE95.8060409@zigo.dhs.org>
Date: Sat, 27 Jan 2007 08:26:13 +0100
From: Dennis Bjorklund <db@zigo.dhs.org>
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To: Carlos Moreno <moreno_pg@mochima.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Seqscan/Indexscan still a known issue?
References: <45BAB682.6060709@mochima.com>
In-Reply-To: <45BAB682.6060709@mochima.com>
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Carlos Moreno skrev:

> When I force it via  "set enable_seqscan to off", the index scan
> takes about 0.1 msec  (as reported by explain analyze), whereas
 >
> For the time being, I'm using an explicit "enable_seqscan off"
> in the client code, before executing the select.  But I wonder:
> Is this still an issue, or has it been solved in the latest
> version?

For most queries it has never been an issue. Every once in a while there 
is a query that the planner makes a non-optimal plan for, but it's not 
that common.

In general the optimizer has improved with every new version of pg.

Almost everyone I've talked to that has upgraded has got a faster 
database tham before. It was like that for 7.4->8.0, for 8.0->8.1 and 
for 8.1->8.2. So in your case going from 7.4->8.2 is most likely going 
to give a speedup (especially if you have some queries that isn't just 
simple primary key lookups).

In your case it's hard to give any advice since you didn't share the 
EXPLAIN ANALYZE output with us. I'm pretty sure it's possible to tune pg 
so it makes the right choice even for this query of yours but without 
the EXPLAIN ANALYZE output we would just be guessing anyway. If you want 
to share it then it might be helpful to show the plan both with and 
without seqscan enabled.

How often do you run VACUUM ANALYZE; on the database?

/Dennis