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Oracle Tips by Burleson 

Oracle Streams
Chapter 4 - Capture and Propagate Configuration

Capture Process Rule Evaluation

When the changes are extracted from the redo log file by the Capture process, the changes are put thorough a series of rule evaluation steps. The Capture process evaluates a change against the negative rule set first. When one or more rules in the negative rule set evaluate to TRUE for the change, the change is discarded. When one or more rules in the positive rule set evaluate to TRUE for the change, the change satisfies the positive rule set and it is retained for enqueue.

The first step is to perform Pre-Filtering in which a Capture process evaluates rules in its rule sets at the object level and schema level.  The goal is to place changes found in the redo log into two categories: changes that should be converted into LCRs and changes that should not be converted into LCRs.

The Pre-Filtering process is done with incomplete information. A change is converted into a LCR when the change satisfies the rule sets. In case of MAYBE evaluations against both the positive and negative rule sets, the change is converted to an LCR for further evaluation.

Next, LCR-Filtering is performed.  This is when a Capture process evaluates rules against information in each LCR to separate the LCRs into two categories: LCRs that should be enqueued, and LCRs that should be discarded.

The Capture process then discards the LCRs that should not be enqueued and enqueues the LCRs that have qualified into the Queue associated with the Capture process.

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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