| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Rick Otten <rottenwindfish(at)gmail(dot)com> |
| Cc: | "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Queries intermittently slow |
| Date: | 2016-01-07 18:34:51 |
| Message-ID: | 13016.1452191691@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
Rick Otten <rottenwindfish(at)gmail(dot)com> writes:
> On Thu, Jan 7, 2016 at 12:51 PM, Scott Rankin <srankin(at)motus(dot)com> wrote:
>> Winner! Both of those settings were set to always, and as soon as I
>> turned them off, the query times smoothed right out.
> Is this generally true for all PostgreSQL systems on Linux, or only for
> specific use cases?
It's fairly well established that the implementation of transparent
huge pages in Linux kernels from the 2.6-or-so era sucks, and you're
best off turning it off if you care about consistency of performance.
I am not sure whether modern kernels have improved this area.
I think you can get an idea of how big a problem you have by noting
the accumulated runtime of the khugepaged daemon.
(BTW, it would likely be a good thing to collect some current wisdom
in this area and add it to section 17.4 of our docs.)
regards, tom lane
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