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Home -> Community -> Usenet -> c.d.o.server -> Re: lots of waiting on 'db file parallel write'
"peter" <p_msantos_at_yahoo.com> wrote:
> Folks,
> I'm currently trying to get to the bottom of why my 4 database
> writters spend so much time
> waiting on 'db file parallel write'... even when it appears that the
> system is not terribly busy.
>
> Environment:
> Oracle 10.1.0.4
> Solaris 8 - 64bit
> IBM SAN T700
> Veritas filesystem (mostly everything is 0+1 raid with a few luns at
> raid 5).
> 4 db writters
>
> So at different times during the day I notice that the system just
> "hangs". When I check what is
> waiting I see the number of wait seconds on my dbwn processes is
> anywhere from 10-140 seconds.
What do you mean by that? That the current wait they are in has been going on for 10 to 140 seconds? That they have waited that much time cumulative (and if so, since when?)
> Obviously if the db writters can go fast enough, the I start to see
> sessions pile up and
> lots of waits on 'free buffer wait'.
>
> Something interesting in the AWR reports....
Since "free buffer wait" don't appear in this report, I doubt it is all that useful, as the data from normal times is drowning data from the "hung" times. (But your redo generation rate is shockingly out of step with the rest, it seems to me.)
...
>
> truss on one of the db writers.
Rather than trussing one, how about tracing it from Oracle? Specifically, I'd want to know the distribution of the db file parallel writes during the hung periods. Are you having lots of moderately slow waits, or lots of fast waits with one or two extremely slow ones?
Xho
-- -------------------- http://NewsReader.Com/ -------------------- Usenet Newsgroup Service $9.95/Month 30GBReceived on Mon Feb 27 2006 - 20:41:29 CST