Introduction
In this chapter, the extensions to the
Apply process will be presented through the creation of suitable
user-defined procedures called the Apply handlers. In earlier
chapters, the fact that the Apply process is an optional Oracle
background process was presented. The Apply process dequeues
logical change records and user messages from a specific queue.
The following sections also cover some
sample procedures that are used as the handler routines.
Apply Process and Apply Handlers
The Apply process dequeues the LCRs and
user messages from a queue. When the Apply process dequeues, the
events may be applied to database objects directly as
transactions or may be passed on as the parameters to
user-defined procedures. These procedures are the user-defined
Apply handlers. The database changes may include the DML or DDL
changes.
Figure 6.1 Apply Process and Apply Handlers
As shown in Figure 6.1, Apply handlers
typically include a DML handler, a DDL handler, a Message
handler and Pre-Commit handlers. The concept of handlers has
been introduced in previous chapters.
