Friday, September 21, 2012

High ENQ:SQ contention in database

This Happened recently when all of a sudden Database stopped responding.

Only option left was to bounce the DB. Since it is a RAC setup, we shutdown one of the instance first and fortunately after starting things came to normal.

Later on when i analyzed the AWR of Database, first instance i found ENQ:SQ contention in top events.

This was new for me, then i checked TOP SQL section of AWR.

Here all top queries were accessing a particular Sequence , when i checked this sequence it was newly created and the cache size was very less 10.

So as such i increased cache size to 100 initially, and till now things are working fine.

I think it was because of this particular sequence , and this should not occur again.

Will try to dig out more..about it...

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