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Re: Estimating WAL volume

From: "Simon Riggs" <simon(at)2ndquadrant(dot)com>
To: "Greg Smith" <gsmith(at)gregsmith(dot)com>
Cc: <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Estimating WAL volume
Date: 2007-07-16 08:02:08
Message-ID: 1184572928.5125.4.camel@ebony.site (view raw or flat)
Thread:
Lists: pgsql-performance
On Wed, 2007-07-11 at 23:10 -0400, Greg Smith wrote:
> All this talk of WAL writing lately has me wondering something I haven't 
> spent enough time looking at the source to figure out myself this 
> week...any good rules of thumb out there for estimating WAL volume?  I'm 
> used to just measuring it via benchmarking but it strikes me a formula 
> would be nice to have for pre-planning.
> 
> For example, if I have a table where a typical row is X bytes wide, and 
> I'm updating Y of those per second, what's the expected write rate of WAL 
> volume?  Some % of those writes are going to be full pages; what's 
> typical? How much does the number and complexity of indexes factor into 
> things--just add the width of the index in bytes to the size of the 
> record, or is it worse than that?

I published an analysis of WAL traffic from Greg Stark earlier, based
upon xlogdump.

http://archives.postgresql.org/pgsql-hackers/2007-03/msg01589.php

Other details of WAL volumes are in the code. Further analysis would be
welcome, to assist discussions of where to optimize next.

-- 
  Simon Riggs
  EnterpriseDB  http://www.enterprisedb.com


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