Re: Weird failure in explain.out with OpenBSD

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Michael Paquier <michael(at)paquier(dot)xyz>
Cc: Postgres hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Weird failure in explain.out with OpenBSD
Date: 2020-12-29 21:16:06
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I wrote:
> ... so my guess is that something messed up in transmitting or combining a
> parallel worker's execution time.

Hmph, no, a look at explain.c shows that the "Execution Time" is just
based on the difference of INSTR_TIME_SET_CURRENT measurements taken
within the current process. It's difficult to conclude anything except
that the clock went backwards. Which is weird, because according to [1]
that system does have clock_gettime(CLOCK_MONOTONIC), which'd be our
preferred choice of INSTR_TIME time base; and such clocks are not
supposed to go backwards ever.

Tis puzzling, but it's hard to avoid the suspicion of a kernel bug.

regards, tom lane


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