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
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.