From: Craig James <craig_james@emolecules.com>
To: Josh Berkus <josh@agliodbs.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: PostgreSQL as a local in-memory cache
Date: Wed, 16 Jun 2010 12:36:31 -0700
Message-ID: <4C1927BF.9030708@emolecules.com> (raw)
In-Reply-To: <4C191F46.4060408@agliodbs.com>
References: <cb0fb58c-9134-4314-a1d0-08fc39f911a6@40g2000pry.googlegroups.com>
<87bpbcpabg.fsf@cbbrowne-laptop.afilias-int.info>
<4C17A417.2040600@noao.edu>
<87ocfcnqmk.fsf@cbbrowne-laptop.afilias-int.info>
<4C180A3B.7090905@agliodbs.com>
<4634b12c-749f-4605-9d95-121b8e2bd9e4@k17g2000pro.googlegroups.com>
<4C191F46.4060408@agliodbs.com>
On 6/16/10 12:00 PM, Josh Berkus wrote:
>
>> * fsync=off => 5,100
>> * fsync=off and synchronous_commit=off => 5,500
>
> Now, this *is* interesting ... why should synch_commit make a difference
> if fsync is off?
>
> Anyone have any ideas?
I found that pgbench has "noise" of about 20% (I posted about this a couple days ago using data from 1000 identical pgbench runs). Unless you make a bunch of runs and average them, a difference of 5,100 to 5,500 appears to be meaningless.
Craig
>
>> tmpfs, WAL on same tmpfs:
>> * Default config: 5,200
>> * full_page_writes=off => 5,200
>> * fsync=off => 5,250
>> * synchronous_commit=off => 5,200
>> * fsync=off and synchronous_commit=off => 5,450
>> * fsync=off and full_page_writes=off => 5,250
>> * fsync=off, synchronous_commit=off and full_page_writes=off => 5,500
>
> So, in this test, it seems like having WAL on tmpfs doesn't make a
> significant difference for everything == off.
>
> I'll try running some tests on Amazon when I have a chance. It would be
> worthwhile to get figures without Python's "ceiling".
>
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To: pgsql-performance@postgresql.org
Cc: craig_james@emolecules.com, josh@agliodbs.com
Subject: Re: PostgreSQL as a local in-memory cache
In-Reply-To: <4C1927BF.9030708@emolecules.com>
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