Oracle Database 11g: Performance Student Guide

Objectives

• After completing this lesson, you should be able to:
• Describe enhancements to locking mechanisms
• Use the enhanced PL/SQL recompilation mechanism
• Create and use invisible indexes
• Describe Adaptive Cursor Sharing
• Manage your SPFILE

Oracle Database 11g supports online redefinition for tables with materialized views and view
logs. In addition, online redefinition supports triggers with the FOLLOWS or PRECEDES clause,
which establishes an ordering dependency between the triggers.
In previous database versions, all directly and indirectly dependent views and PL/SQL packages
would be invalidated after an online redefinition or other DDL operations. These views and
PL/SQL packages would automatically be recompiled whenever they are next invoked. If there
are a lot of dependent PL/SQL packages and views, the cost of the revalidation or recompilation
can be significant.
In Oracle Database 11g, views, synonyms, and other table-dependent objects (with the exception
of triggers) that are not logically affected by the redefinition, are not invalidated. So, for example,
if referenced column names and types are the same after the redefinition, then they are not
invalidated.
This optimization is “transparent,” that is, it is turned on by default.
Another example: If the redefinition drops a column, only those procedures and views that
reference the column are invalidated. The other dependent procedures and views remain valid.
Note that all triggers on a table being redefined are invalidated (as the redefinition can potentially
change the internal column numbers and data types), but they are automatically revalidated with
the next DML execution to the table.

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