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Oracle Streams
Chapter 2 - Streams Components and Processes

Custom Apply and Apply Handlers

Figure 2.3 - Apply Process and Apply Handlers


DML Handler

A user procedure can be created that processes row LCRs resulting from DML statements. Such a procedure is called a DML Handler. For each table associated with an apply process, a separate DML handler can be set up to process each of the DML statements in row LCRs.  DML statements include: INSERT, UPDATE, DELETE, and LOB_UPDATE.

DDL Handler

Another procedure that processes DDL LCRs resulting from the DDL statements can be created. Such a procedure is called a DDL Handler.  An Apply process can have many DML handlers but only one DDL handler. Since the DDL is a special database activity that can be used to add or modify the database table structures, it often warrants more planning, coordination and control by administrators. The DDL handler can be used to keep an audit on DDL activities or even to make notifications in case a DDL command is executed.

Message Handler

A Message Handler defined at the apply process will process the user-enqueued event that does not contain an LCR. A message handler is a user-defined procedure that can process non-LCR user messages in a customized way.

The message handler offers advantages in any environment that has applications that need to update one or more remote databases or perform some other remote action.

The above text is an excerpt from:

Oracle Streams
High Speed Replication and Data Sharing

ISBN 0-9745993-5-2

by Madhu Tumma

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