> > I have only one explanation: it reduces number of transactions ready
> > to commit (because of the same FK writers will wait till first one
> > committed - ie log fsynced) and WAL commit performance 
> > greatly depends on how many commits were done by single log fsync.
> > 7.0.3+nofsync commit performance doesn't depend on this factor.
> 
> Sure, but that's not exactly a fair comparison is it?  7.0.3+nofsync
> should be compared against 7.1+nofsync.  I put the pg_fsync routine
> back in a little while ago, so nofsync should work again.

But I tested old 7.1 (fsync) version -:)

And we always will have to enable fsync when comparing our
performance with other DBes.

> It occurs to me though that disabling fsync should probably 
> also reduce the WAL commit delay to zero, no?  What is the default

I think so.

> commit delay now?

As before 5 * 10^(-6) sec - pretty the same as sleep(0) -:)
Seems CommitDelay is not very useful parameter now - XLogFlush
logic and fsync time add some delay.

Vadim

Fri, 8 Dec 2000 17:39:38 -0800 
"Mikheev, Vadim" <vmikheev@SECTORBASE.COM>
RE: 7.0.3(nofsync) vs 7.1 
"Mikheev, Vadim" <vmikheev@SECTORBASE.COM> writes:
> And we always will have to enable fsync when comparing our
> performance with other DBes.

Of course, but when people say "it's slower than 7.0.3+nofsync"
I think that turning off fsync makes a fairer comparison there.


>> also reduce the WAL commit delay to zero, no?  What is the default

> I think so.

>> commit delay now?

> As before 5 * 10^(-6) sec - pretty the same as sleep(0) -:)
> Seems CommitDelay is not very useful parameter now - XLogFlush
> logic and fsync time add some delay.

There was a thread recently about smarter ways to handle shared fsync
of the log --- IIRC, we talked about self-tuning commit delay, releasing
waiting processes as soon as someone else had fsync'd, etc.  Looks like
none of those ideas are in the code now.  Did you not like any of those
ideas, or just no time to work on it yet?

			regards, tom lane

Fri, 08 Dec 2000 20:58:36 -0500
Tom Lane <tgl@sss.pgh.pa.us>
Re: 7.0.3(nofsync) vs 7.1 