From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: Greg Stark <stark@mit.edu>,
        PostgreSQL-development <pgsql-hackers@postgresql.org>,
        Haribabu Kommi <kommi.haribabu@gmail.com>
Subject: Re: gettimeofday is at the end of its usefulness?
In-reply-to: <20161227091737.5jlcbu4rnqpv2k77@alap3.anarazel.de>
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Comments: In-reply-to Andres Freund <andres@anarazel.de>
	message dated "Tue, 27 Dec 2016 01:17:37 -0800"
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Date: Tue, 27 Dec 2016 10:50:27 -0500
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Andres Freund <andres@anarazel.de> writes:
> On 2016-12-27 01:35:05 +0000, Greg Stark wrote:
>> On Dec 26, 2016 10:35 PM, "Tom Lane" <tgl@sss.pgh.pa.us> wrote:
>>> So it seems like the configure support we'd need is to detect
>>> whether clock_gettime is available (note on Linux there's also
>>> a library requirement, -lrt), and we would also need a way to
>>> provide a platform-specific choice of clockid; we at least need
>>> enough smarts to use CLOCK_MONOTONIC_RAW on macOS.

>> This seems like something that really should be checked at runtime.

> I'm pretty strongly against doing performance measurements at
> startup. Both the delay and the potential for differing test results
> seem like pretty bad consequences.

Yeah, that doesn't sound great to me either.  And I don't entirely
see the point, at least not with what we know now.  I am a bit concerned
that we'll find out there are popular platforms where clock_gettime
compiles but fails with ENOSYS, or some similarly unhelpful behavior.
But we won't find that out if we don't try.

			regards, tom lane


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