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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: (view raw or whole 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.

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

  Simon Riggs

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