Date: Sat, 29 Oct 2005 23:43:22 +0200 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: John-Mark Gurney <gurney_j@resnet.uoregon.edu> Cc: Pertti Kosunen <pertti.kosunen@pp.nic.fi>, Robert Watson <rwatson@FreeBSD.org>, David Xu <davidxu@FreeBSD.org>, "Yuriy N. Shkandybin" <jura@networks.ru>, current@FreeBSD.org Subject: Re: Timers and timing, was: MySQL Performance 6.0rc1 Message-ID: <43332.1130622202@critter.freebsd.dk> In-Reply-To: Your message of "Sat, 29 Oct 2005 14:05:50 PDT." <20051029210550.GV4115@funkthat.com>
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In message <20051029210550.GV4115@funkthat.com>, John-Mark Gurney writes: >This also gets into the question how do you round a second? :) I had this discussion with Bruce some years back and the (or at least my) answer is: you don't round timestamps, you truncate. My argument for this is what's commonly called "times arrow" mandates truncation instead of rounding. Rounding is about finding the nearest point of a lower resolution and this is fine for meter, lightyears, money and so on where reality is isotropic. But time never goes backwards. We don't know why, but it just doesn't [1]. Because of this, it only makes sense (IMO) to truncate, because that ensures that we never get a timestamp in the future [2] >If you cared that much that you were .001 seconds after 124, you'd be >using a more acurate clock... It's not if you care about the delay, it's if you compare output from time(2) to clock_gettime()... Poul-Henning [1] No, I don't want to discuss if gravity is the accumulation of time in an Einsteinian geometry, much less if the Aliens taught the ancient egyptians how to reverse time so that the pyramid could be completed before pharao died. [2] If our timestamps had operated in a signed fraction fashion (ie: as in "ten minutes to noon") it would be an entirely different situation, but then I think more people than me would be cursing POSIX. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
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