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To: "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Subject: Re: Postgres refusing to use >1 core
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Date: Wed, 11 May 2011 13:06:53 +0200
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From: "Pierre C" <lists@peufeu.com>
Message-ID: <op.vvbc5r1ieorkce@apollo13>
In-Reply-To: <4DC9E733.8040809@postnewspapers.com.au>
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> I suspect your app is doing lots of tiny single-row queries instead of
> efficiently batching things. It'll be wasting huge amounts of time
> waiting for results. Even if every query is individually incredibly
> fast, with the number of them you seem to be doing you'll lose a LOT of
> time if you loop over lots of little SELECTs.

Using unix sockets, you can expect about 10-20.000 queries/s on small  
simple selects per core, which is quite a feat. TCP adds overhead, so it's  
slower. Over a network, add ping time.

In plpgsql code, you avoid roundtrips, data serializing, and context  
switches, it can be 2-4x faster.

But a big SQL query can process millions of rows/s, it is much more  
efficient.