DB2 on P7 system, System CPU may spike.

If there are many CPUs(over 64 CPUs or even to 200 CPUs) on AIX platform, there might be a performance problem(very high CPU) caused by bad performance of thread_unlock during very high db2 latch contention.

The main symptom at db2 side is sqloSpinLockReleaseConflict will cost a long time(over 100 microseconds) to release a latch and many latch-waiters are waiting on this latch.

The root cause is AIX kernel call thread_unlock(called by db2 function sqloSpinLockReleaseConflict) does not provide good performance in extreme high workload. The solution is applying AIX fix and DB2 fix together.


Below is the AIX APAR information.

6.1 TL06 SP7 (IV10411)
6.1 TL07 SP2 (IV10010)
6.1 TL08  (IV13362)
7.1 GA SP5 (IV14638)
7.1 TL01 SP2 (IV09962)


Below is the corresponding DB2 APAR information.

DB2 v97 APAR is IC79285, which is expected to be fixed in v97fp6. This APAR will provide fix to implement AIX new API thread_unlock_extended(). After installing db2 fix, to make use of new AIX API thread_unlock_extended, a new db2 registry variable is needed to be turned on.

db2set DB2_ENABLE_THREAD_UNLOCK_EXTENDED=YES
db2start