Vishal Desai systematically troubleshooted an interesting case where the initial symptoms of the problem showed a spike of enq: SQ – contention waits, but he dug deeper – and found the root cause to be quite different. He followed the blockers of waiting sessions manually to reach the root cause – and also used my @ash/ash_wait_chains.sql and @ash/event_hist.sql scripts to extract the same information more conveniently (note that he had modified the scripts to take AWR snap_ids as time range parameters instead of the usual date/timestamp):
- http://vishaldesai.wordpress.com/2015/04/24/wait-chain-analysis-using-tanels-awesome-ash_wait_chains-script/
Definitely worth a read if you’re into troubleshooting non-trivial performance problems :)
