Message-ID: <69c579d91f1c94a283be562e2ba4ffdb.squirrel@sq.gransy.com>
In-Reply-To: <000001cf1671$c5e023b0$51a06b10$@uni-konstanz.de>
References: <000001cf1671$c5e023b0$51a06b10$@uni-konstanz.de>
Date: Tue, 21 Jan 2014 11:57:51 +0100
Subject: Re: Increasing query time after updates
From: "Tomas Vondra" <tv@fuzzy.cz>
To: "Katharina Koobs" <katharina.koobs@uni-konstanz.de>
Cc: pgsql-performance@postgresql.org,
 "'Sebastian Vogt'" <sebastian.vogt@uni-konstanz.de>
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Hi,

On 21 Leden 2014, 7:26, Katharina Koobs wrote:
> Hi,
>
> We have a PostgreSQL DB, version 8.4 on a Suse Linux system.
> Every night a script runs with several updates and inserts. The query time
> at day increases after
> approximately 3 weeks from a few minutes to about an hour.
> After export, drop and import the DB the query time is again at a few
> minutes.
>
> We have tested vacuum full, vacuum analyze and reindex and get no
> improvement.
>
> Has anyone an idea why the queries are getting slower and slower?

The table/index bloat would be my first bet, but that should be fixed (or
at least improved) by the vacuum commands you've tested.

Sadly, the amount of info you provided is insufficient to determine the
cause - the best thing you can give us are explain plans of the query, one
when it's fast, one when it's slow.

If it's longer than a few lines, please post it to explain.depesz.com and
not here (the clients will reformat it, making it unreadable).

> Thank you so much for your help!
>
> The DB configuration:
>
> Virtual server, 7GB RAM, DB size = 16GB
>
> shared_buffers = 1024MB
> temp_buffers = 32MB
> work_mem = 8MB
> checkpoint_segments = 20
> effective_cache_size = 512MB

Any reason not to use higher value for effective_cache_size? You have 7GB
of RAM, 1GB of that is for shared buffers, so I'd say ~4GB would be a good
value here. Unlikely to be the cause of the issues you're seeing, though.

Tomas


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