The Apply process is an optional Oracle
background process that dequeues LCRs and user messages from a
specific queue. It then either applies each one directly or
passes it as a parameter to a user-defined procedure, called a
handler. The Apply process is basically a part of the consumer
of or subscriber to the database changes. In other words, it is
an end point in the data replication flow.
The Main Features of the Apply Process
The Apply process is implemented as an
Oracle background process, whose process name is Annn, in
which nnn is an Apply process number. The Apply process
is the process which consumes the LCR events or user messages.
In other words, it is a dequeuing process.
When dequeued by the Apply process, captured events, such as the
LCRs, contain the DML changes or DDL changes that need to be
applied to the destination database objects. The Apply process
directly dequeues and implements the database changes. The apply
user applies all row changes resulting from DML operations and
all DDL changes.
A single Apply process can apply either
captured events or user-enqueued events, but it cannot do both.
If a queue at a destination database contains both captured and
user-enqueued LCRs, the destination database must have at least
two Apply processes to process the events. The Apply process can
be associated with a SYS.AnyData queue, but it cannot be
associated with a typed queue. The Apply process applies the
changes based on the rules that are defined by the DBA. When the
rule condition evaluates to TRUE, the changes are applied. Based
on the rules evaluation, changes are either applied or