Slow queries after vacuum analyze

Hello,

I have a customer that experience a strange behaviour related to statictics.

Threre is a vacuum analyze planned during the night.
The morning, 1 day out of 2, there are some extremely slow queries.
Those queries lasts more than 5 minutes (never waited more and cancelled
them) whereas when everything is OK they last less than 300ms.

In order to resolve this i have to execute a least one analyze, sometimes
more.

My Configuration:
Windows
PostgreSQL 8.4.8
default_statistics_target = 100

In addition to an increase for shared_buffers, work_mem, ..., i changed
the default_statistics_target to 500 with no effect.
It was even worse as i never managed to get rid of the slow queries after
running many analyze.
So i fell back to default_statistics_target=100 in order to get rid of
those slow queries.

I have no idea of what i can do to solve this issue.
Any help would be greatly appreciated.

Cordialement,
*Ghislain ROUVIGNAC*
Ingénieur R&D
ghr(at)sylob(dot)com

7 rue Marcel Dassault - Z.A. La Mouline - 81990 Cambon d'Albi - FRANCE
Tel : 05 63 53 08 18 - Fax : 05 63 53 07 42 - www.sylob.com
Support : 05 63 53 78 35 - support(at)sylob(dot)com
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