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#1 (**permalink**) 04-18-2008, 11:04 AM

> > I'm hoping someone can shed some light on these results.
>
> Not without a lot more detail on how you *got* the results.
> What exactly did you do to force the various plan choices?
> (I see some ridiculous choices of indexscans, for instance,
> suggesting improper use of enable_seqscan in some cases.)
> And what's the "cache rows" and "disk rows" stuff, and how do
> you know that what you were measuring is actually what you
> think it is? I have zero confidence in Windows-atop-ATA as a
> platform for measuring disk-related behaviors, because I
> don't think you can control or even know what caching is going on.

You can control the writeback-cache from Device Manager->(the
disk)->Policies. And if that is turned off, fsync definitly should write
through, just as on *nix. (write-cache is on by default, no surprise)

AFAIK, you can't control what is cached for reading.

//Magnus

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TIP 8: explain analyze is your friend

#2 (**permalink**) 04-18-2008, 11:04 AM

Magnus Hagander wrote:
> > > I'm hoping someone can shed some light on these results.
> >
> > Not without a lot more detail on how you *got* the results.
> > What exactly did you do to force the various plan choices?
> > (I see some ridiculous choices of indexscans, for instance,
> > suggesting improper use of enable_seqscan in some cases.)
> > And what's the "cache rows" and "disk rows" stuff, and how do
> > you know that what you were measuring is actually what you
> > think it is? I have zero confidence in Windows-atop-ATA as a
> > platform for measuring disk-related behaviors, because I
> > don't think you can control or even know what caching is going on.
>
> You can control the writeback-cache from Device Manager->(the
> disk)->Policies. And if that is turned off, fsync definitly should write
> through, just as on *nix. (write-cache is on by default, no surprise)
>
> AFAIK, you can't control what is cached for reading.

Are you saying that fsync() doesn't write to the platters by default on
Win32?

--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073

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