Several months have passed since my previous “mutex wait” post. I was so busy with work and conference presentations. Thanks to all my listeners at UKOUG2011, Hotsos2012 and Medias2012 conferences and several seminars for inspiring questions and conversations.
I. Unexpected change.
Now it is time to discuss how contemporary Oracle waits for mutexes. My previous posts described evolution of “invisible and aggressive” 10.2-11.1 mutex waits into fully accounted and less aggressive 11gR2 mutexes. Surprisingly Oracle 18.104.22.168.2 (or 22.214.171.124 PSU2) appeared in April 2011 demonstrated almost negligible CPU consumption during mutex waits. (more…)
I would like to describe how Oracle versions 126.96.36.199-188.8.131.52.1 waited for mutexes. This algorithm also appears to be used in post-184.108.40.206.2 PSUs and new 220.127.116.11 patchset as _mutex_wait_scheme=0.
My previous post demonstrated that before version 11.2:
- “Cursor: pin S” was pure wait for CPU. Long “cursor: pin S” waits indicated CPU starvation.
- Mutex contention was almost invisible to Oracle Wait Interface
- Spin time to acquire mutex was accounted as CPU time. It was service time, not waiting time.
Things changed. Mutex waits in Oracle 11.2 significantly differ from previous versions. Contemporary mutex waits are not CPU aggressive anymore, completely visible to Oracle Wait Interface and highly tunable.