Date: Thu, 15 May 2014 13:21:08 +0200
From: Andres Freund <andres@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@postgreSQL.org
Subject: Re: gettimeofday is at the end of its usefulness?
Message-ID: <20140515112108.GM23943@awork2.anarazel.de>
References: <31856.1400021891@sss.pgh.pa.us>
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Hi,

On 2014-05-13 18:58:11 -0400, Tom Lane wrote:
> Anyway it looks like clock_gettime() might be worth using on Linux
> just for the more precise output.  It doesn't seem to exist on OS X
> though, and I have no idea about elsewhere.

Agreed that using clock_gettime() would be a good idea. I'd say we
should have a wrapper around it that is able to provide nanosecond
precision. If only gettimeofday() (and whatever windows is using) is
available, we can dynamically fall back to that.

> I'm curious if anybody has ideas about other things we might do for
> portable high-precision timing.

It's far from a solve-it-all, but can we perhaps try to coalesce
repeated time measurements? We'll very frequently do a
    InstrStopNode();
    /* minimal amount of work */
    InstrStartNode();
which will measure the time twice. I think there's a fair number of
scenarios where once would be enough. I'll freely admit that I haven't
looked enough to determine how we could do that API wise.

Greetings,

Andres Freund

-- 
 Andres Freund	                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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