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Re: how to fix problem then when two queries run at the same time, it takes longer to complete then if run in sequence

From: Albert Cervera Areny <albert(at)sedifa(dot)com>
To: pgsql-performance(at)postgresql(dot)org, Miernik <public(at)public(dot)miernik(dot)name>
Subject: Re: how to fix problem then when two queries run at the same time, it takes longer to complete then if run in sequence
Date: 2008-07-24 07:38:28
Message-ID: 200807240938.28482.albert@sedifa.com (view raw or flat)
Thread:
Lists: pgsql-performance
A Dimecres 23 Juliol 2008, Miernik va escriure:
> I have a PostgreSQL database on a very low-resource Xen virtual machine,
> 48 MB RAM. When two queries run at the same time, it takes longer to
> complete then if run in sequence. Is there perhaps a way to install
> something like a query sequencer, which would process queries in a FIFO
> manner, one at a time, even if a new query comes before the last one
> running is finished, it would not give the new query to the server
> before the one running now finishes? That would greatly improve
> performance.

You didn't mention your PostgreSQL version. Since 8.3 there's "synchronized 
scans" which greatly improves performance if concurrent queries have to do a 
sequential scan on the same table. Of course, if queries don't hit the same 
table there'll be no improvements in performance...

>
> Any tips in general for running PostgreSQL on such low-resource machine?
>
> I have:
>
> shared_buffers = 5MB
> work_mem = 1024kB
>
> are these good values, or could perhaps changing something improve it a
> bit? Any other parameters to look at?
>
> --
> Miernik
> http://miernik.name/




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