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Wednesday, January 3, 2018

                                                   

                                                             Library cache lock



What is  "Library cache lock" ?

This event controls the concurrency between clients of the library cache. It acquires a lock on the object handle so that either:
  • One client can prevent other clients from accessing the same object.
  • The client can maintain a dependency for a long time (for example, so that no other client can change the object).
This lock is also obtained to locate an object in the library cache.
Library cache lock will be obtained on database objects referenced during parsing or compiling of SQL or PL/SQL statements (table, view, procedure, function, package, package body, trigger, index, cluster, synonym). The lock will be released at the end of the parse or compilation.

Cursors (SQL and PL/SQL areas), pipes and any other transient objects do not use this lock.
Library cache lock is not deadlock sensitive and the operation is synchronous.

Parameters:
  • handle address:
    Address of the object being loaded.
  • lock address:
    Address of the load lock being used. This is not the same thing as a latch or an enqueue, it is a State Object.
  • Mode:
    Indicates the data pieces of the object which need to be loaded.
  • Namespace:
    The name of the object namespace as it is displayed in V$DB_OBJECT_CACHE view

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