Re: Slow copy with little CPU/disk usage

От: Jim C. Nasby
Тема: Re: Slow copy with little CPU/disk usage
Дата: ,
Msg-id: 20050420222227.GW58835@decibel.org
(см: обсуждение, исходный текст)
Ответ на: Re: Slow copy with little CPU/disk usage  (Mischa Sandberg)
Список: pgsql-performance

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Slow copy with little CPU/disk usage  ("Jim C. Nasby", )
 Re: Slow copy with little CPU/disk usage  (Tom Lane, )
  Re: Slow copy with little CPU/disk usage  (Mischa Sandberg, )
   Re: Slow copy with little CPU/disk usage  ("Jim C. Nasby", )
 Re: Slow copy with little CPU/disk usage  (Greg Stark, )
  Re: Slow copy with little CPU/disk usage  ("Jim C. Nasby", )

No, this is a single process. And there's known issues with context
storms on Xeons, so that might be what you're seeing.

On Tue, Apr 19, 2005 at 09:37:21PM -0700, Mischa Sandberg wrote:
> Quoting Tom Lane <>:
>
> > "Jim C. Nasby" <> writes:
> > > A friend of mine has an application where he's copying in 4000 rows at a
> > > time into a table that has about 4M rows. Each row is 40-50 bytes. This
> > > is taking 25 seconds on a dual PIII-1GHz with 1G of RAM and a 2 disk
> > > SATA mirror, running FBSD 4.10-stable. There's one index on the table.
> >
> > If there's no hidden costs such as foreign key checks, that does seem
> > pretty dang slow.
> >
> > > What's really odd is that neither the CPU or the disk are being
> > > hammered. The box appears to be pretty idle; the postgresql proces is
> > > using 4-5% CPU.
> --
> This sounds EXACTLY like my problem, if you make the box to a Xeon 2.4GHz, 2GB
> RAM ... with two SCSI drives (xlog and base); loading 10K rows of about 200
> bytes each; takes about 20 secs at the best, and much longer at the worst. By
> any chance does your friend have several client machines/processes trying to
> mass-load rows at the same time? Or at least some other processes updating
> that table in a bulkish way? What I get is low diskio, low cpu, even low
> context-switches ... and I'm betting he should take a look at pg_locks. For my
> own problem, I gather that an exclusive lock is necessary while updating
> indexes and heap, and the multiple processes doing the update can make that
> pathological.
>
> Anyway, have your friend check pg_locks.
>
>
> "Dreams come true, not free." -- S.Sondheim, ITW
>

--
Jim C. Nasby, Database Consultant               
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