From: Albert Cervera Areny <albert@sedifa.com>
Organization: Sedifa, S.L.
To: pgsql-performance@postgresql.org,
 Miernik <public@public.miernik.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: Thu, 24 Jul 2008 09:38:28 +0200
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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/