Re: pgbench throttling latency limit

From: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
To: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>, Andres Freund <andres(at)anarazel(dot)de>
Cc: PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pgbench throttling latency limit
Date: 2015-10-22 09:37:44
Message-ID: 5628AE68.4090204@lab.ntt.co.jp
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On 2015/10/22 18:20, Fabien COELHO wrote:
>>
>>> progress: 365.0 s, 18392.1 tps, lat 94.857 ms stddev 23.917, lag 90.980
>>> ms, 106244 skipped
>>>
>>> 100k skipped transactions at a rate limit of 40k? That doesn't seem right.
>>
>> Argh. It's just because I used -P5. It's a bit confusing that the other
>> options are per second, and this is per interval...
>
> I agree, but I'm unsure of a fix, beyond what is already done which is to
> show units next to the figures...
>
> ISTM that people expect "tps" for performance, even on several seconds.
> When it comes to skipped transactions, a count seemed more natural. I
> really just see this as an indicator that things are not going smoothly.
>
> Maybe it could be shown as a percentage of scheduled transactions,
> possibly with an option?
>
> A mitigation is to always run with -P 1 :-).

Wouldn't printing average (per second) over the interval work?

Thanks,
Amit

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