Oracle Tips by Burleson

Oracle10g Grid Computing with RAC
Chapter 7 - Cache Fusion and Inter Instance Coordination

Enqueues

The resources managed by the GES include the following:

Transaction locks – It is acquired in the exclusive mode when a transaction initiates its first row level change. The lock is held until the transaction is committed or rolled back.

Library Cache locks - When a database object (such as a table, view, procedure, function, package, package body, trigger, index, cluster, or synonym) is referenced during parsing or compiling of a SQL, DML or DDL, PL/SQL, or Java statement, the process parsing or compiling the statement acquires the library cache lock in the correct mode.

Dictionary Cache Locks - Global enqueues are used in the cluster database mode. The data dictionary structure is the same for all Oracle instances in a cluster database, as it is for instances in a single-instance database. However, in real application clusters, Oracle synchronizes all the dictionary caches throughout the cluster. Real application clusters use latches to do this, just as in the case of a single-instance Oracle database.