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Re: Inserting 8MB bytea: just 25% of disk perf used?

From: Florian Weimer <fweimer(at)bfk(dot)de>
To: Matthew Wakeling <matthew(at)flymine(dot)org>
Cc: "fkater\(at)googlemail(dot)com" <fkater(at)googlemail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Inserting 8MB bytea: just 25% of disk perf used?
Date: 2010-01-21 16:24:12
Message-ID: 82bpgnh1eb.fsf@mid.bfk.de (view raw or flat)
Thread:
Lists: pgsql-performance
* Matthew Wakeling:

> The data needs to be written first to the WAL, in order to provide
> crash-safety. So you're actually writing 1600MB, not 800.

In addition to that, PostgreSQL 8.4.2 seems pre-fill TOAST files (or
all relations?) with zeros when they are written first, which adds
another 400 to 800 MB.

-- 
Florian Weimer                <fweimer(at)bfk(dot)de>
BFK edv-consulting GmbH       http://www.bfk.de/
Kriegsstraße 100              tel: +49-721-96201-1
D-76133 Karlsruhe             fax: +49-721-96201-99

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