LogMiner automatically builds its own internal dictionary from the LogMiner dictionary that you specify when you start LogMiner (either an online catalog, a dictionary in the redo log files, or a flat file). This dictionary provides a snapshot of the database objects and their definitions.
If your LogMiner dictionary is in the redo log files or is a flat file, then you can use the DDL_DICT_TRACKING option to the PL/SQL DBMS_LOGMNR.START_LOGMNR procedure to direct LogMiner to track data definition language (DDL) statements. DDL tracking enables LogMiner to successfully track structural changes made to a database object, such as adding or dropping columns from a table. For example:
EXECUTE DBMS_LOGMNR.START_LOGMNR(OPTIONS => - DBMS_LOGMNR.DDL_DICT_TRACKING + DBMS_LOGMNR.DICT_FROM_REDO_LOGS);
See "Example 5: Tracking DDL Statements in the Internal Dictionary" for a complete example.
With this option set, LogMiner applies any DDL statements seen in the redo log files to its internal dictionary.
In general, it is a good idea to keep supplemental logging and the DDL tracking feature enabled, because if they are not enabled and a DDL event occurs, then LogMiner returns some of the redo data as binary data. Also, a metadata version mismatch could occur.
When you enable DDL_DICT_TRACKING, data manipulation language (DML) operations performed on tables created after the LogMiner dictionary was extracted can be shown correctly.
For example, if a table employees is updated through two successive DDL operations such that column gender is added in one operation, and column commission_pct is dropped in the next, then LogMiner will keep versioned information for employees for each of these changes. This means that LogMiner can successfully mine redo log files that are from before and after these DDL changes, and no binary data will be presented for the SQL_REDO or SQL_UNDO columns.
Because LogMiner automatically assigns versions to the database metadata, it will detect and notify you of any mismatch between its internal dictionary and the dictionary in the redo log files. If LogMiner detects a mismatch, then it generates binary data in the SQL_REDO column of the V$LOGMNR_CONTENTS view, the INFO column contains the string "Dictionary Version Mismatch", and the STATUS column will contain the value 2.
It is important to understand that the LogMiner internal dictionary is not the same as the LogMiner dictionary contained in a flat file, in redo log files, or in the online catalog. LogMiner does update its internal dictionary, but it does not update the dictionary that is contained in a flat file, in redo log files, or in the online catalog.
The following list describes the requirements for specifying the DDL_DICT_TRACKING option with the DBMS_LOGMNR.START_LOGMNR procedure.
The DDL_DICT_TRACKING option is not valid with the DICT_FROM_ONLINE_CATALOG option.
The DDL_DICT_TRACKING option requires that the database be open.
Supplemental logging must be enabled database-wide, or log groups must have been created for the tables of interest.