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Oracle Tips by Burleson |
Oracle Streams
Chapter 9 -
Streams and Real Application Cluster
Capture and Apply Processes in a RAC
Instance
Whenever an instance in an Oracle RAC cluster
fails, the instance is recovered immediately by another instance in
the cluster. The following actions occur that affect the Streams
environment:
-
Each queue owned by the failed
instance is assigned to a new instance.
-
The Capture process is restarted
automatically on the instance that now owns the queue. If the failed
instance is brought back online later, the Capture process does not
move back to the original instance. Even though the failed instance
was running the Capture process at the time of failure, it is no
longer the owner of the queue used by the Capture process. This is
the normal behavior unless it is altered by the alter_queue_table
procedure, which is explained in a later section.
-
All propagation jobs are
automatically migrated to the new instance from the failed instance.
The SYS.AnyData queues can be configured on any
instances within the RAC database. Only the owner instance may have
a buffer for a queue, but different instances may have buffers for
different queues. A buffered queue is System Global Area (SGA)
memory associated with a SYS.AnyData queue that contains only
captured events.
Figure 9.2 shows that instance DNYDBA2A has the
SYS.AnyData and the associated buffers.
Figure 9.2 Streams in a RAC environment
Only the instance that has the queue, and
therefore the buffers, can propagate and receive the LCR events.
Each of the propagations that propagate captured events to a RAC
destination database must use an instance-specific database link
that refers to the owner instance of the destination queue. If the
propagation connects to any other instance, the propagation will
raise an error.
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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