Re: X$ksmsp (OSEE 10.2.0.2 on Solaris 8)

A couple of months ago, Oracle Support sent me a query to run against x$ksmsp in order to identify shared pool fragmentation. They assured me that any problems with querying x$ tables were from earlier versions of Oracle. The local technical sales rep also assured us that there should be no issues. I was born in the morning but I wasn't born YESTERDAY morning, so I was nervous about querying that table directly and, after testing the query in a non-Production environment, verified that, not only did the query hold the shared pool latch, but it took an hour for the query to run. Couldn't log onto the database from another session. Could have been quite painful in Production.

Incidently, we seem to have reached reasonable stability in our 10.1.0.3 RAC environment. After suffering for months with instance crashes due to ORA-04031, Oracle Support recommended that we set _lm_res_cache_cleanup=70. We implemented that in early May and haven't had any crashes since. We do still have a possible memory leak due to automatic statistics gathering which shows up as a continually increasing value for MISCELLANEOUS in V$SGASTAT for the shared pool. When it reaches 900-Mb (of 1300-Mb shared_pool_size), we plan an off-hour bounce of that instance. Takes about 6 weeks for MISCELLANEOUS to reach 900-Mb. The other two instances in the cluster don't seem to have the same problem. Those instances have been up for almost 8 weeks now. Instances used to crash after 3 weeks on average. Database stability is a wonderful thing.

Regards,
Mark Strickland
Next Online Technologies
Seattle, WA

On 6/28/06, Schultz, Charles <sac_at_uillinois.edu> wrote:
>
> I looked at v$sgastat, but it is was too general. We have fragmentation
> issues (in the shared pool, I believe) and Oracle is saying that we have
> a potential memory leak (still in the diagnosis phase). Hence, I think
> the PGA and Buffer pool views are out, although I could be wrong. The
> ora-4031 trace files are reporting errors on the following objects:
> kggfaAllocSeg
> kgghtInit
> kgghteInit
> qcdlgcd
> qcopCreateCol
> qcopCreateLog
> qcuAllocIdn
> qkshtQBAtomicAlloc
> qkxrMemAlloc
>
> Of course, one of the most confusing problems with this fragmentation
> issue is whether to decrease or increase the shared pool. Increasing the
> shared pool has the temporary affect of making the ora-4031 errors
> disappear, but that seems to be a bad long-term solution, as decreasing
> the shared pool might actually be the better way to go. My one caveat
> with this approach (resizing the shared pool) ignores the root cause of
> the problem - if the fragmentation is avoidable, why not avoid it? I am
> still trying to learn more about this concept - even though I have read
> a lot (Tom Kyte, Jonathan Lewis, etc), the material is sinking in
> slowly. From talks I have had offline, this might be a case of
> contention on a shared pool heap latch - a requestor wants a certain
> size chunk and the latch for the size chunk is busy. My memory of the
> details might be fuzzy.
>
>
> I ran across note 367392.1, but all of our traces are from foreground
> processes, not background.
>
> Following note 146599.1, I peeked at V$SHARED_POOL_RESERVED but did not
> learn much (one size that has failed a number of times, 4200). Also,
> this note points to the x$ tables, hence my original question about
> x$ksmsp. If the performance is so bad and there are better alternatives,
> I am surprised that they are not listed here.
>
> And finally note 62143.1. I am still re-reading this one, as I still
> have much to learn in "tuning the shared pool". This is a good appendix
> for terms and offers various scripts, but none that I found to be very
> relevant.
>
> Other references:
> "Understanding Shared Pool Memory Structures" Russell Green, Sep 2005
> Oracle white paper
> Scripts from Alejandro Vargas' blog
>
> -----Original Message-----
> From: Mladen Gogala [mailto: gogala_at_sbcglobal.net]
> Sent: Tuesday, June 27, 2006 7:47 PM
> To: Schultz, Charles
> Cc: duncan.lawie_at_credit-suisse.com; Hallas, John, Tech Dev;
> oracle-l_at_freelists.org
> Subject: Re: X$ksmsp (OSEE 10.2.0.2 on Solaris 8)
>
>
> On 06/27/2006 10:30:11 AM, Schultz, Charles wrote:
> > What is the alternative to track down memory issues? Sure, one could
> > use DMA (Direct Memory Access), but I for one am not there yet. If
> > there is a better way to diagnose and resolve memory issues, I am all
> > ears (or rather, eyes *grin*).
> >
>
> Track what memory issues? Insufficient shared pool? Try with V$SGASTAT.
> PGA? Try with V$PROCESS_MEMORY. Buffer cache? Try with
> V$BUFFER_POOL_STATISTICS.
> What do you have in mind when you say "memory issues"? All those tables
> are well documented and stable.
>
> --
> Mladen Gogala
> http://www.mgogala.com
>
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>

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