The DB2 log contains information about updates, deletes, and inserts on DB2 tables. The DB2 log contains information about additional changes and events; this additional information is not currently replicated.
DB2 logs changes to rows in DB2 tables as they occur. The information written to the log includes copies of the data before and after the changes. In DB2, these records are known as “undo” and “redo” records.
Control records are written for begins, commits, and aborts. These records are translated to begins, commits, and rollbacks.
The DB2 log is composed of a series of data sets. Replication Extract uses these log data sets to identify DB2 data changes. The DB2 log consists of three types of data sets:
Active log data sets reside on a direct access storage device (DASD). As changes occur, they are first recorded in an active log data set. Eventually, the active log fills and DB2 copies the log to an archive log.
Archive log data sets reside on DASD or tape.
The bootstrap data set (BSDS) contains information about all of the active and archive data sets that make up the log records.
Since DB2 writes change records to the active log as they occur, Replication Extract can process the log records immediately after they are entered.
Typically, DB2 writes two copies of the logs for redundancy in the event of log data set corruption.
