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тАО09-30-2003 02:48 AM
тАО09-30-2003 02:48 AM
sar shows zero idle
http://forums.itrc.hp.com/service/forums/questionanswer.do?threadId=226549
My Oracle financials, running on an N class takes a performance hit sometimes in late morning early afternoon. It is when concurrent manager gets over 20 requests, (currently we have 35 in the queue)
Attached is are sars during the 'event'
-b -M -d.
The disk i/o and cache hit rates remain relatively constant throughout the day.
The big clue is the sar output showing waiting for i/o being less than 1%.
Oracle is pulling somethings into memory, and processing them ( ineffiently? thrashing? deadlocks? )
This looks like an index problem, but the DBA's explain plan shows indexes being used (i'm told) and when the concurrent manager queue drops below 20, the sar 'waiting for i/o' will raise, like any behaved database should.
This is what starts the finger pointing to my EVA dirves as the culprit as described in the link above.
What tools can I use to find out whats going on here. I have Oracle Enterprise Manager, but am below novice level in it's use.
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тАО09-30-2003 03:02 AM
тАО09-30-2003 03:02 AM
Re: sar shows zero idle
This should give some information re resource utilisation.
Rgds,
Jean-Luc
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тАО09-30-2003 03:12 AM
тАО09-30-2003 03:12 AM
Re: sar shows zero idle
system has 24 gig ram.
32 bit oracle, so our SGA is around 1.7 gig
shmmax is currently 4.8 gig.
Is there a way to confirm this guess? Can I see shared memory utilization / shortages?
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тАО09-30-2003 03:24 AM
тАО09-30-2003 03:24 AM
Re: sar shows zero idle
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тАО09-30-2003 03:25 AM
тАО09-30-2003 03:25 AM
Re: sar shows zero idle
It would also be good to know if you are seeing a high context switch rate (Glance or sar -w).
Also attach a kmtune output.
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тАО09-30-2003 03:27 AM
тАО09-30-2003 03:27 AM
Re: sar shows zero idle
http://forums1.itrc.hp.com/service/forums/parseCurl.do?CURL=%2Fcm%2FQuestionAnswer%2F1%2C%2C0x8f2e8f960573d611abdb0090277a778c%2C00.html&admit=716493758+1064935262507+28353475
What is the database size ?
Any chance to run statspack and post the results ?
Rgds,
Jean-Luc
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тАО09-30-2003 03:49 AM
тАО09-30-2003 03:49 AM
Re: sar shows zero idle
here as sar -w from yesterday, followed by today, then a kmtune output.
I'm off to Glance land...
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тАО09-30-2003 04:04 AM
тАО09-30-2003 04:04 AM
Re: sar shows zero idle
Memory is defined as RAM plus swap.
Here is an Oracle tuning doc, for what its worth.
http://www2.itrc.hp.com/service/cki/search.do?category=c0&docType=Security&docType=Patch&docType=EngineerNotes&docType=BugReports&docType=Hardware&docType=ReferenceMaterials&docType=ThirdParty&searchString=UPERFKBAN00000726&search.y=8&search.x=28&mode=id&admit=-1335382922+1064937766794+28353475&searchCrit=allwords
It was written by a guy who helped us with some Oracle performance problems.
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тАО09-30-2003 05:05 AM
тАО09-30-2003 05:05 AM
Re: sar shows zero idle
The 64-bit code doesn't execute faster (it's actually slower than 32-bit code) BUT because resource limits -- like maximum addressable space -- are gone the overall performance can increase dramitically in application which require large amounts of resources -- e.g. Oracle.
If you are stuck in 32-bit land then I can suggest one thing that may help. Install all the latest LVM / JFS / SCSI performance patches for 11.0. Next increase your buffer cache. I would suggest that you do it with a non-zero bufpages rather than dynamic buffer cache because we want to eliminate as much kernel overhead as possible. The idea is that we are going to partially address the limited SGA buffer size by using UNIX buffer cache as well. 11.11 systems actually perform better using cooked files and well-patched 11.00 systems may perform better under Oracle with cooked files as well. Normally, I limit 11.00 buffer cache to about 800MB (yours is currently 1200; 5% of 24GB) but in your case I would try 1600MB (or so -- bufpages=409600) and look for any improvement. Surprisingly, you might actually find the reverse to be true and that the best performance is found somewhere around 600MB --- if the system is spending a lot of time searching the buffer cache it may be faster to get the data directly from the disk array -- which itself is cached.
Now having said all this, I think the real problem is in the SQL/application code itself especially because the CPU's are spending so much time in user (rather than system) mode.
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тАО09-30-2003 05:49 AM
тАО09-30-2003 05:49 AM
Re: sar shows zero idle
Any hints in here as to the combination of events that triggers our slowdown?