Re: posix advises ...

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.
>
> --
> * Greg Smith [email protected] http://www.gregsmith.com  
> Baltimore, MD
>
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