> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
> Sent: Monday, March 07, 2005 4:57 PM
> To: John A Meinel
> Cc: Dave Held; pgsql-performance@postgresql.org;
> pgsql-hackers-win32@postgresql.org
> Subject: Re: [pgsql-hackers-win32] [PERFORM] Help with tuning
> this query
> (with
>
> John A Meinel <john@arbash-meinel.com> writes:
> > Dave Held wrote:
> >> There is always clock().
>
> > My experience with clock() on win32 is that CLOCKS_PER_SEC
> > was 1000, and it had a resolution of 55clocks / s.

Which is why I suggested QueryPerformanceCounter for Win32. I
only suggested clock() for *nix.

> The other problem is it measures process CPU time, not elapsed time
> which is probably more significant for our purposes.

Actually, the bigger problem is that a quick test of clock() on
Linux shows that it only has a maximum resolution of 10ms on my
hardware. Looks like gettimeofday() is the best choice.

> Which brings up a question: just what does QueryPerformanceCounter
> measure?

I think it measures raw CPU cycles, roughly, which seems like it
would more or less correspond to wall time.

__
David B. Held
Software Engineer/Array Services Group
200 14th Ave. East, Sartell, MN 56377
320.534.3637 320.253.7800 800.752.8129

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