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Re: pg_test_timing tool for EXPLAIN ANALYZE overhead

From: Marti Raudsepp <marti(at)juffo(dot)org>
To: Greg Smith <greg(at)2ndquadrant(dot)com>
Cc: Jay Levitt <jay(dot)levitt(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, ants(dot)aasma(at)eesti(dot)ee
Subject: Re: pg_test_timing tool for EXPLAIN ANALYZE overhead
Date: 2012-02-22 17:25:24
Message-ID: CABRT9RDAYnK87Z=pxaSEzYJPZhz95cKEOzZ6W22wYbH2pU5Rew@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Wed, Feb 22, 2012 at 18:44, Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
> As far as I've been able to tell, there aren't any issues unique to Windows
> there.  Multiple cores can have their TSC results get out of sync on Windows
> for the same reason they do on Linux systems, and there's also the same
> frequency/temperature issues.

Not on recent Linux kernel versions. Linux automatically detects when
the TSC is unstable (due to power management or out-of-sync
cores/sockets) and automatically falls back to the more expensive HPET
or ACPI methods.

e.g:
% dmesg |grep -i tsc
[    0.000000] Fast TSC calibration using PIT
[    0.164075] checking TSC synchronization [CPU#0 -> CPU#1]: passed.
[    0.197062] Switching to clocksource tsc
[    0.260960] Marking TSC unstable due to TSC halts in idle

Whether these tests cover 100% of the possible conditions, and whether
the detection has race conditions or not, I don't know.

Regards,
Marti

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