|From:||Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>|
|To:||Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>|
|Cc:||nagata(at)sraoss(dot)co(dot)jp, gregsmithpgsql(at)gmail(dot)com, pgsql-hackers(at)postgresql(dot)org, david(dot)christensen(at)crunchydata(dot)com|
|Subject:||Re: pgbench logging broken by time logic changes|
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>>> I cannot say that I'm thrilled by having multiple tv stuff back in several
>>> place. I can be okay with one, though. What about the attached? Does it
>>> make sense?
> +1 The patch rounds down sd->start_time from ms to s but it seems to
> me a degradation.
Yes, please we should not use time.
>> At first, I also thought of fixing pg_time_now() to use gettimeofday() instead
>> of INSTR_TIME_SET_CURRENT, but I noticed that using INSTR_TIME_SET_CURRENT is
>> proper to measure time interval. I mean, this macro uses
>> lock_gettime(CLOCK_MONOTONIC, ) if avilable, which give reliable interval
>> timing even in the face of changes to the system clock due to NTP.
> If I understand the op correctly, the problem here is the time values
> in pgbench log file are based on a bogus epoch.
It is not "bogus", but is not necessary epoch depending on the underlying
function called behind by INSTR_TIME macros, and people are entitled to
expect epoch for log correlations.
> If it's the only issue
> here and and if we just want to show the time based on the unix epoch
> time, just recording the difference would work as I scketched in the
> attached. (Precisely theepoch would move if we set the system clock
> but I don't think that matters:p)
I do like the approach.
I'm hesitant to promote it for fixing the beta, but the code impact is
small enough, so I'd say yes. Maybe there is a similar issue with progress
which should probably use the same approach. I think that aligning the
implementations can wait for pg15.
The patch as white space issues. Attached an updated version which fixes
that, adds comments and simplify the code a little bit.
> I'm not sure we have transaction lasts for very short time that
> nanoseconds matters.
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