Re: Estimating WAL volume

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