Capture Process Rule Evaluation
Figure 4.4 shows the evaluation process
graphically.
Figure 4.4 Rule Evaluation Flow
LogMiner Data Dictionary
The Capture process makes use of a data
dictionary, which is different from the source database data
dictionary. This special data dictionary is called the LogMiner
Data Dictionary. The Capture process requires a LogMiner data
dictionary because the information in the primary data
dictionary may not match the changes being captured from the
redo log. These changes may have occurred minutes, hours, or
even days before they are captured by a Capture process. This is
important in the sense that when the actual capture takes place,
it needs to have the right dictionary information. Since the
timing of the Capture process and timing of the actual database
table change can be different, the maintenance of the log
dictionary, which can provide time sensitive dictionary
information, becomes significant.
The first time a Capture process is started
at the database, Oracle uses the extracted data dictionary
information in the redo log to create a LogMiner data
dictionary. This dictionary is separate from the primary data
dictionary for the source database. Additional Capture processes
may use this existing LogMiner data dictionary, or they may
create new LogMiner data dictionaries.
Since the Capture process can have its own
timing, when it does extract and create the LCRs, the object’s
structure in the primary dictionary may not match. The Capture
process cannot depend on the primary data dictionary, especially
when it is stopped for some time. This is the reason that the
LogMiner Data Dictionary is maintained.
