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Re: Checkpoint cost, looks like it is WAL/CRC

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: josh(at)agliodbs(dot)com
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Checkpoint cost, looks like it is WAL/CRC
Date: 2005-07-22 23:11:36
Message-ID: 17262.1122073896@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Josh Berkus <josh(at)agliodbs(dot)com> writes:
>> Um, where are the test runs underlying this spreadsheet?  I don't have a
>> whole lot of confidence in looking at full-run average TPM numbers to
>> discern whether transient dropoffs in TPM are significant or not.

> Web in the form of: 
> http://khack.osdl.org/stp/#test_number#/

> Where #test_number# is:

> Machine0, no patch:
> 302904
> 302905
> 302906

> Machine0, patch:
> 301901
> 302902
> 302903

> Machine2, no patch:
> 302910
> 302911
> 302912

> Machine2, patch:
> 301907
> 302908
> 302909

Hmm.  Eyeballing the NOTPM trace for cases 302912 and 302909, it sure
looks like the post-checkpoint performance recovery is *slower* in
the latter.  And why is 302902 visibly slower overall than 302905?
I thought for a bit that you had gotten "patch" vs "no patch" backwards,
but the oprofile results linked to these pages look right: XLogInsert
takes significantly more time in the "no patch" cases.

There's something awfully weird going on here.  I was prepared to see
no statistically-significant differences, but not multiple cases that
seem to be going the "wrong direction".

BTW, I'd like to look at 302906, but its [Details] link is broken.

			regards, tom lane

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Next:From: Josh BerkusDate: 2005-07-22 23:29:57
Subject: Re: Checkpoint cost, looks like it is WAL/CRC
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Subject: Re: Autovacuum loose ends

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