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тАО09-27-2002 08:37 AM
тАО09-27-2002 08:37 AM
Oracle I/O related problems
I see in global waits on glance (semaphore 92% blocked on IO 1.9% ). What does that mean? We tried all possible things from database side. Is there anything I can do from unix side?
Thanks for your info. in advance.
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тАО09-27-2002 09:08 AM
тАО09-27-2002 09:08 AM
Re: Oracle I/O related problems
Ted
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тАО09-27-2002 09:41 AM
тАО09-27-2002 09:41 AM
Re: Oracle I/O related problems
Database is on: L class server(4cpu,16GB RAM);Uses EMC storage with SRDF(synchronous); Uses raw devices; Produces 30GB of redo everyday.
We see hell lot of "logfile sync" wait events in database.
We do not use Async IO.
Any pointers to where/what to look at?
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тАО09-27-2002 12:44 PM
тАО09-27-2002 12:44 PM
Re: Oracle I/O related problems
You should try to look at the performance on the Symmetrix (specifically the SRDF portion) to see if that is your problem. Do you have WorkLoad Analyzer that you can use to get statistics from the Symmetrix?
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тАО09-27-2002 12:45 PM
тАО09-27-2002 12:45 PM
Re: Oracle I/O related problems
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тАО09-27-2002 01:23 PM
тАО09-27-2002 01:23 PM
Re: Oracle I/O related problems
Waiting on semaphore indicates that there are hot tables in the database and log sync as well. Try to adjust them on different disks. Also your SRDF background event is also contributing it.
EMC does not recommend, but we are doing striping of the logical volumes on XPs here. It seems to yield significant performance increase. Particularly you may want to try to stripe your redo log lvols. Though the LUNs (volumes) are striped in side the disk system, lvol striping will further improve performance if you chose your stripe based on the stripe of RAID.
Did you try using file systems for the database?. With online JFS you get the mincache=direct and convosync=direct so that you will get the same raw functionality. File systems are more manageable from the sysadmin's perspective.
-Sri
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тАО09-30-2002 08:40 AM
тАО09-30-2002 08:40 AM
Re: Oracle I/O related problems
with 30GB of redo each day, how big are your online relogfiles ?
Each logswitch will force a checkpoint, so if you have small redologs, your databasebuffer will be flushed to disk all the time. with 30GB of redo each day, I'd recommend to have 200MB-500MB online redologfiles and may be up to 6 groups.
This will give you 60-150 logswitches a day, which might be still too many.
Hope this helps
Volker
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тАО09-30-2002 09:27 AM
тАО09-30-2002 09:27 AM
Re: Oracle I/O related problems
suggestions. Some more details about my databases.
redolog size is 500Mb, there are 15 memebers. It switches a log every 7 min. in peak time. Implemented SAME methodology (stripe and mirror everything) stripe size 64kb. planning to go for 1MB. We know SRDF is a bottleneck. Moving to latest series. If you guys can help me to speed up lgwr I will be happy. log_buffers=1MB. Our problems are redolog,lgwr oriented. There is no way to use parallelism in lgwr. what else I have to do?