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Re: Free WAL caches on switching segments

From: Mark Kirkwood <markir(at)paradise(dot)net(dot)nz>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, daveg <daveg(at)sonic(dot)net>, ITAGAKI Takahiro <itagaki(dot)takahiro(at)lab(dot)ntt(dot)co(dot)jp>, pgsql-patches(at)postgresql(dot)org
Subject: Re: Free WAL caches on switching segments
Date: 2006-02-14 21:50:27
Message-ID: 43F250A3.6020304@paradise.net.nz (view raw or flat)
Thread:
Lists: pgsql-patches
Tom Lane wrote:
> Mark Kirkwood <markir(at)paradise(dot)net(dot)nz> writes:
> 
>>Tom Lane wrote:
>>
>>>Sounds like a recipe for ensuring it never will be tested.  What's
>>>needed here is some actual tests, not preparation...
> 
> 
>>Does the OP have a test scenario that those of us with appropriate OS's 
>>could try? Come to think of it, what are the appropriate OS's? (I see 
>>NetBSD mentioned so I suppose all the *BSDs, but what others?).
> 
> 
> The test run by the OP was just pgbench, 

Ah - right, missed that sorry.

> which is probably not the
> greatest scenario for showing the benefits of this patch, but at least
> it's neutral ground.  You need a situation in which the kernel is under
> memory stress, else early free of disk cache buffers isn't going to make
> any difference whatever --- so choose a pgbench scale factor that makes
> the database noticeably larger than the test machine's RAM.  Other than
> that, follow the usual guidelines for producing trustworthy pgbench
> numbers: number of clients smaller than scale factor, number of
> transactions per client at least 1000 or so (to eliminate startup
> transients), repeat test a couple times to make sure numbers are
> reproducible.
>

Thinking about this, presumably any write intensive, multi-user 
benchmark would seem to be suitable, so would something like OSDL's 
DBT-2 actually be better to try?

Cheers

Mark

(P.s - academic in my case, unless I try out the latest NetBSD or Linux 
on one of my FreeBSD boxes....)

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