DB2 low CPU low IO (low insert,low update) why ?

[silverman]

Hi,
Im facing a very strange problem with DB2.
when my app reach a certain number of concurrence (not much about 50) the performance of all DB2 systems decreases for Insert and Update statments.
I cheched CPU and IO from all cpus and Disks CPU times dont reach 30% and disks Busy dont reach 10%.
Any Hints ?
Thanks a lot.

[rjr1328]

Since you are not running out of CPU or IO, I would be inclined to think you are running out of some resource. Check the "GET DB CONFIG FOR <dbname>" to review if there are enough agents, memory, connections, etc. You could use the DB2 trace facility to see if you are hitting some limit. Also check the DBDIAG.LOG for any errors/warnings.

Hope this helps

[kazam]

I/O overhead could be because of insufficient page cleaning.

If DB2 agent needs to write a page and if there's no free page in the bufferpool, then the agent must first create a room in the bufferpool by writing a dirty page out of the pool. This will cause the application to stop processing transactions because DB2 agent has to get a free page first and then continue. Hence I/O bottleneck.

CPU overheads could be because of large table scan operations in bufferpool.
Not using indexes, etc.

You can refer to this best practices document for more details on "Tuning and Monitoring database system performance"

http://download.boulde r.ibm.com/ibmdl/pub/software/dw/dm/db2/bestpractices/DB2BP_System_Pe rformance_0508I .pdf

Thanks,
Madhavi.