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Re: Slow indexscan

From: Michael Glaesemann <grzm(at)seespotcode(dot)net>
To: Mikko Partio <mpartio(at)gmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Slow indexscan
Date: 2007-06-20 16:53:44
Message-ID: A52DA702-F83C-4DC0-BBD6-49D7FC075A2B@seespotcode.net (view raw or flat)
Thread:
Lists: pgsql-performance
On Jun 20, 2007, at 9:02 , Mikko Partio wrote:

> Relevant facts:
> pg version 7.3.4 (yeah very old, we are upgrading asap)

There have been many performance improvements—not to mention security  
and data-eating bug fixes—since then. Upgrading should be one of your  
highest priorities. And it may even fix the issue at hand!

> Index Scan using tbl_20070601_pkey on tbl_20070601 t1
> (cost=0.00..365.13rows=13 width=137) (actual time=
> 120.83..10752.64 rows=539 loops=1)

Something appears a bit off with your index, or at least the  
statistics Postgres is using to estimate it. It's estimating that the  
query will return 13 rows, but you're actually returning 539. Maybe  
there's some corruption in the index which is leading to both the  
performance issue you're seeing and the statistics issues. Have you  
tried REINDEX?

Michael Glaesemann
grzm seespotcode net



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