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Don Burleson Blog 







 dbms_shared_pool.markhot tips

Oracle Database Tips by Donald BurlesonMarch 23, 2015

Question:  How does the procedure dbms_shared_pool.markhot work? 

Answer:  The dbms_shared_pool.markhot procedure is new in 11g r2 and marks a library cache object as a "hot" object in an attempt to reduce "mutex contention" wait events in Oracle 11g r2 and beyind.

There is also dbms_shared_pool.unmarkhot procedure to unmark the hot object in the library cache.  See MOSC Note 727400.1 titled "WAITEVENT: "library cache: mutex X" for additional details on using the markhot and unmarkhot procedures.

Here is an example of using the dbms_shared_pool markhot procedure.  This is ud in a database startup trigger, just like dbms_shared_pool_keep.

 exec dbms_shared_pool.markhot('SYS','DBMS_APPLICATION_INFO',1);

Oracle guru Andrey S. Nikolaev notes that dbms_shared_pool.markhot is related to a hidden parameter _kgl_hot_object_copies:

By default, Oracle created approximately "number of CPU Cores" hot objects copies. This observation should be further investigated.

You can adjust this number by _kgl_hot_object_copies parameter. Therefore if you prefer not to use hidden parameters, the dbms_shared_pool.markhot() can help you to resolve mutex contention.

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