Message-ID: <4F7CD40E.10401@agliodbs.com>
Date: Wed, 04 Apr 2012 16:06:54 -0700
From: Josh Berkus <josh@agliodbs.com>
Organization: PostgreSQL Experts Inc.
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To: pgsql-hackers@postgresql.org, Jignesh Shah <jkshah@gmail.com>
Subject: Re: patch: improve SLRU replacement algorithm
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On 4/4/12 4:02 PM, Tom Lane wrote:
> Greg Stark <stark@mit.edu> writes:
>> On Wed, Apr 4, 2012 at 9:34 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
>>> Why is this pgbench run accessing so much unhinted data that is > 1
>>> million transactions old? Do you believe those numbers? Looks weird.
> 
>> I think this is in the nature of the workload pgbench does. Because
>> the updates are uniformly distributed, not concentrated 90% in 10% of
>> the buffers like most real-world systems, (and I believe pgbench only
>> does index lookups) the second time a tuple is looked at is going to
>> average N/2 transactions later where N is the number of tuples.
> 
> That's a good point, and it makes me wonder whether pgbench is the right
> test case to be micro-optimizing around.  It would be a good idea to at
> least compare the numbers for something with more locality of reference.

Jignesh, would DVDstore help for this?


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