From: fkater@googlemail.com <fkater@googlemail.com>
To: Matthew Wakeling <matthew@flymine.org>
Cc: pgsql-performance@postgresql.org
Subject: Re: Inserting 8MB bytea: just 25% of disk perf used?
Date: Thu, 14 Jan 2010 21:18:54 +0100
Message-ID: <20100114201854.GC2384@comppasch2> (raw)
In-Reply-To: <alpine.DEB.2.00.1001141458590.6195@aragorn.flymine.org>
References: <20100114142903.GB2973@comppasch2>
<alpine.DEB.2.00.1001141458590.6195@aragorn.flymine.org>
Thanks a lot for the detailed reply.
Matthew Wakeling:
> On Thu, 14 Jan 2010, fkater@googlemail.com wrote:
> > This takes about 50s, so, 800MB/50s = 16MB/s.
> >
> > However the harddisk (sata) could write 43 MB/s in the worst
> > case! Why is write performance limited to 16 MB/s?
>
> Several reasons:
>
> The data needs to be written first to the WAL, in order to provide
> crash-safety. So you're actually writing 1600MB, not 800.
I understand. So the actual throughput is 32MB/s which is
closer to 43 MB/s, of course.
Can I verify that by temporarily disabling WAL writes
completely and see if the thoughput is then doubled?
Felix
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To: pgsql-performance@postgresql.org
Cc: fkater@googlemail.com, matthew@flymine.org
Subject: Re: Inserting 8MB bytea: just 25% of disk perf used?
In-Reply-To: <20100114201854.GC2384@comppasch2>
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