On 04/05/2012 02:23 PM, Jim Nasby wrote:
> If there's a fundamental flaw in how linux deals with heavy writes that
> means you can't rely on certain latency windows, perhaps we should be
> looking at using a different OS to test those cases...
Performance under this sort of write overload is something that's been a
major focus of more recent Linux kernel versions than I've tested yet.
It may get better just via the passage of time. Today is surely far
improved over the status quo a few years ago, when ext3 was the only
viable filesystem choice and tens of seconds could pass with no activity.
The other thing to recognize here is that some heavy write operations
get quite a throughput improvement from how things work now, with VACUUM
being the most obvious one. If I retune Linux to act more like other
operating systems, with a smaller and more frequently flushed write
cache, it will trash VACUUM write performance in the process. That's
one of the reasons I submitted the MB/s logging to VACUUM for 9.2, to
make it easier to measure what happens to that as write cache changes
are made.
--
Greg Smith 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.com
