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Re: wal_buffers, redux

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: wal_buffers, redux
Date: 2012-03-12 17:55:26
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Lists: pgsql-hackers
On Mon, Mar 12, 2012 at 12:32 PM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
> On Nate Boley's machine, the difference was ~100% increase rather than
> ~10%.

Oh, right.  I had forgotten how dramatic the changes were in those
test runs.  I guess I should be happy that the absolute numbers on
this machine were as high as they were.  This machine seems to be
beating that one on every metric.

> Do you think the difference is in the CPU architecture, or the
> IO subsystem?

That is an excellent question.  I tried looking at vmstat output, but
a funny thing kept happening: periodically, the iowait column would
show a gigantic negative number instead of a number between 0 and 100.
 This makes me a little chary of believing any of it.  Even if I did,
I'm not sure that would fully answer the question.  So I guess the
short answer is that I don't know, and I'm not even sure how I might
go about figuring it out.  Any ideas?

> Also, do you have the latency numbers?

Not at the moment, but I'll generate them.

Robert Haas
The Enterprise PostgreSQL Company

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