If you have problems with high contention on hot library cache objects that leads to excessive “Library cache: mutex X” event, you probably already know about library cache enhancements in 11.2.0.2 and _kgl_debug / dbms_shared_pool.markhot(). If not – there is a very good blog of Andrey Nikolaev –
http://andreynikolaev.wordpress.com about latches and mutexes that is definitely worh reading.
We had some “Library cache: mutex X” and tried _kgl_debug for several hottest objects and that actually resolved the issue.
However later we trapped two interesting bugs.
The first one was fake ” ORA-01918: user ” does not exist ” error when we tried to drop / create
objects in schema wich already had several objects listed in _kgl_debug parameter. We used markhot() instead of the hidden parameter (and it’s suppose to be a more correct anyway) and the issue is gone.
The second one caused
ORA-7445 [pfrsepmd_entrypoint_metadata]
errors and it looks like a subject to Bug 10188716 – ORA-7445 [pfrsepmd_entrypoint_metadata] if PLSQL object is marked HOT [ID 10188716.8] and it is fixed in 11.2.0.3.
agorbyk 