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Home -> Community -> Mailing Lists -> Oracle-L -> Re: X$ksmsp (OSEE 10.2.0.2 on Solaris 8)
This is my first post here, pardon me if I sent it
incorrectly.
Memory chunk allocation/de-allocation is protected by 7 shared pool latches, although it uses one latch to start with, and as the number of memory chunks increases Oracle vertically partitions the shared pool with more latches up to a maiximum of 7.
You can see how many shared pool latches are in effect by running "select count(distinct ksmchidx) from x$ksmsp" query.
If you suspect shared pool memory is leaking and if you can afford to go after x$ksmsp as it has potential to cause database outage, periodically run the following query:
select ksmchcom, ksmchcls, sum(ksmchsiz), count(*) from x$ksmsp;
and look for any abnormal trend. For example, Oracle 8i had a bug on permanent memory and in that case, total permanent memory from x$ksmsp would go up over time.
Total shared pool reported in x$ksmsp would be more than actual shared pool setting because memory required for database block buffer header's and other fixed arrays are also included in that.
HTH,
Sai.
http://sai-oracle.blogspot.com
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$SGASTAT for the shared pool. When it reaches 900-Mb
(of 1300-Mb
shared_pool_size), we plan an off-hour bounce of that
instance. Takes about
6 weeks for MISCELLANEOUS to reach 900-Mb. The
other two instances in the
cluster don't seem to have the same problem. Those
instances have been up
for almost 8 weeks now. Instances used to crash after
3 weeks on average.
Database stability is a wonderful thing.
Regards,
Mark Strickland
Next Online Technologies
Seattle, WA
On 6/28/06, Schultz, Charles <sac_at_xxxxxxxxxxxxx> wrote:
I looked at v$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$ksmsp. If the performance is so bad and there are better alternatives,
I am surprised that they are not listed here.
And finally note 62143.1. I am still re-reading this one, as I still
have much to learn in "tuning the shared pool". This is a good appendix
for terms and offers various scripts, but none that I found to be very
relevant.
Other references:
"Understanding Shared Pool Memory Structures"
Russell Green, Sep 2005
Oracle white paper
Scripts from Alejandro Vargas' blog
-----Original Message-----
From: Mladen Gogala [mailto: gogala_at_xxxxxxxxxxxxx]
Sent: Tuesday, June 27, 2006 7:47 PM
To: Schultz, Charles
Cc: duncan.lawie_at_xxxxxxxxxxxxxxxxx; Hallas, John,
Tech Dev;
oracle-l_at_xxxxxxxxxxxxx
Subject: Re: X$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.
-- http://www.freelists.org/webpage/oracle-lReceived on Mon Jul 24 2006 - 01:54:28 CDT
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