Re: Investigating IO Saturation

От: Tom Lane
Тема: Re: Investigating IO Saturation
Дата: ,
Msg-id: 19963.1138122458@sss.pgh.pa.us
(см: обсуждение, исходный текст)
Ответ на: Investigating IO Saturation  (Brad Nicholson)
Список: pgsql-performance

Скрыть дерево обсуждения

Investigating IO Saturation  (Brad Nicholson, )
 Re: Investigating IO Saturation  ("Joshua D. Drake", )
  Re: Investigating IO Saturation  (Brad Nicholson, )
   Re: Investigating IO Saturation  ("Joshua D. Drake", )
 Re: Investigating IO Saturation  (Tom Lane, )
 Re: Investigating IO Saturation  (Chris Browne, )
  Re: Investigating IO Saturation  (Andrew Sullivan, )

Brad Nicholson <> writes:
> I'm investigating a potential IO issue.  We're running 7.4 on AIX 5.1.
> During periods of high activity (reads, writes, and vacuums), we are
> seeing iostat reporting 100% disk usage.  I have a feeling that the
> iostat numbers are misleading.  I can make iostat usage jump from less
> than 10% to greater than 95% by running a single vacuum against a
> moderate sized table (no noticeable change in the other activity).

That's not particularly surprising, and I see no reason to think that
iostat is lying to you.

More recent versions of PG include parameters that you can use to
"throttle" vacuum's I/O demand ... but unthrottled, it's definitely
an I/O hog.

The vmstat numbers suggest that vacuum is not completely killing you,
but you could probably get some improvement in foreground query
performance by throttling it back.  There are other good reasons to
consider an update, anyway.

            regards, tom lane


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