Re: Remove or weaken hints about "effective resolution of sleep delays is 10 ms"?

On February 16, 2016 9:06:57 AM GMT+01:00, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>On Wed, Feb 10, 2016 at 5:15 PM, Andres Freund <andres(at)anarazel(dot)de>
>wrote:
>> Hi,
>>
>> Several places in our docs have blurbs like
>>> Note that on many systems, the effective resolution of sleep delays
>is
>>> 10 milliseconds; setting <varname>wal_writer_delay</> to a value
>that
>>> is not a multiple of 10 might have the same results as setting it to
>>> the next higher multiple of 10.
>> Afaik that's not the case on any recent operating system/hardware. So
>> perhaps we should just remove all of those blurbs, or just replace
>them
>> with something like "on some older systems the effective resolution
>of
>> sleep delays is limited to multiples of 10 milliseconds"?
>
>Hmm, is that true? What we do we think the resolution is on modern
>systems? I would not have guessed that to be inaccurate.

Depends in a lot of factors. The biggest being how busy you're system is. On an mostly idle system (i.e. workout so CPUs being overcommitted) you can get resolutions considerably below one millisecond. HPET can get you very low latencies, making OS scheduling latencies the dominant factor, but one that can be tuned.

Andres

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