Re: perplexing performance on AIX

From: John Smith <>
Date: Wed, 7 May 2008 07:46:36 -0500
Message-ID: <>

Do you have a bug number for that one? We do use ASSM.

On Wed, May 7, 2008 at 7:24 AM, Anjo Kolk <> wrote:

> May be related:
> I have a merge statement that sometimes hangs. In fact the Oracle shadow
> is consuming CPU but it doesn't get accounted for in V$sesstat / v$sysstat
> (haven't checked that but I believe that to be the case). So I see this
> shadow process consuming CPU, I took gdb and attached my self and took a
> stack trace. I found that the merge was doing an insert and for that it had
> to find more space in the index. While finding the space it seems to be in a
> tight loop in the space management code for bitmap segments (ASSM). The
> workaround from Oracle is to not use ASSM for the Index. So if your case one
> of the slaves (or coordinators) hits this problem it won't sent a
> completition message to the coordinator. This then could result in the
> behavior that you see.
> Anjo.
> On 5/6/08, John Smith <> wrote:
> > I have been working with an AIX LPAR which has access to 6 CPU's,
> > defaults to 3. Its primarily a data warehouse instance, so we enabled
> > parallel on it and about half of the tables are large, and are
> > range-partitioned on by year, and in some cases sub-partitioned on
> > accounting period (list method).
> >
> > There is plenty of memory (32G), and its on an EMC Clariion storage.
> > However, when we run loads using merge, and in some cases, some very large
> > queries, the queries run for days at a time, but the CPU usage is not all
> > that high (rarely above about 60%).
> >
> > The AWR report (its oracle shows a huge number of wait events
> > on PX Dequeue Credit: Send Blkd. According to the oracle documentation,
> > this is an idle event, but it appears to me that about 2/3 of the available
> > time is spent waiting on this event. Has anyone seen this, or have any idea
> > how to track down what is causing the problem? There are also a large
> > number of IO wait events, but the time is not significant compared to the PX
> > wait event. Is it possible that PX wait event is caused by the IO wait
> > event? If so, how could I track it down?
> >
> --
> Anjo Kolk
> Owner and Founder OraPerf Projects
> tel: +31-577-712000
> mob: +31-6-55340888

Received on Wed May 07 2008 - 07:46:36 CDT

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