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From: Josh Berkus <josh@agliodbs.com>
To: pgsql-performance@postgresql.org
Subject: Re: PostgreSQL as a local in-memory cache
Date: Wed, 16 Jun 2010 12:00:22 -0700
Message-ID: <4C191F46.4060408@agliodbs.com> (raw)
In-Reply-To: <4634b12c-749f-4605-9d95-121b8e2bd9e4@k17g2000pro.googlegroups.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>


> * 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?

> 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".

-- 
                                  -- Josh Berkus
                                     PostgreSQL Experts Inc.
                                     http://www.pgexperts.com

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