On Thu, 26 Apr 2007, Zeugswetter Andreas ADI SD wrote:
> I am not sure that shrinking per WAL record size (other than the full
> page images), e.g. by only logging changed bytes and not whole tuples,
> would have a huge impact on OLTP tx/sec, since the limiting factor is
> IO's per second and not Mb per second.
With the kind of caching controller that's necessary for any serious OLTP
work with Postgres, number of I/Os per second isn't really an important
number. Total volume of writes to the WAL volume can be though. It's
difficult but not impossible to encounter a workload that becomes
bottlenecked by WAL volume on a good OLTP server, particularly because
that's often going to a single or RAID-1 disk. Whether those workloads
also have the appropriate properties such that their WAL could be shrunk
usefully in real-time is a good question.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD