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Re: patch: improve SLRU replacement algorithm

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: pgsql-hackers(at)postgresql(dot)org, Jignesh Shah <jkshah(at)gmail(dot)com>
Subject: Re: patch: improve SLRU replacement algorithm
Date: 2012-04-04 23:06:54
Message-ID: 4F7CD40E.10401@agliodbs.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On 4/4/12 4:02 PM, Tom Lane wrote:
> Greg Stark <stark(at)mit(dot)edu> writes:
>> On Wed, Apr 4, 2012 at 9:34 PM, Simon Riggs <simon(at)2ndquadrant(dot)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

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