good morning,
this is wonderful news.
this is pretty much what we observed as well. the kernel has acted as showstopper for many setups recently. this patch fixed most cases related to kernel read ahead and so on for us.
in fact, posix_fadvise was the only way to prevent a big germany company from replacing postgres with oracle.
the problem was that synchronized scans led to a significant decrease of I/O throughput as the kernel was simply confused by processes concurrently reading the same file.
I hope zoltan's autoconf magic fixes the portability issues.
hans
On Jun 20, 2008, at 1:19 AM, Greg Smith wrote:
On Thu, 19 Jun 2008, Zoltan Boszormenyi wrote:
This patch (revisited and ported to current CVS HEAD) is indeed using
Greg's original patch and also added another patch written by Mark Wong
that helps evicting closed XLOGs from memory faster.
Great, that will save me some trouble. I've got a stack of Linux performance testing queued up (got stuck behind a kernel bug impacting pgbench) for the next couple of weeks and I'll include this in that testing. I think I've got a similar class of hardware as you tested on for initial evaluation--I'm getting around 200MB/s sequential I/O right now out of my small RAID setup,.
I added your patch to the queue for next month's CommitFest and listed myself as the initial reviewer, but a commit that soon is unlikely. Performance tests like this usually take a while to converge, and since this is using a less popular API I expect a round of portability concerns, too.
Where did Marc's patch come from? I'd like to be able to separate out that change from the rest if necessary.
Also, if you have any specific test cases you ran that I could start by trying to replicate a speedup on, those would be handy as well.
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