Log extracts read and transfer relevant database transactions recorded in the database logs to LTM for z/OS. The log extract in Replication Agent is the Replication Extract.
A DB2 table named LTMOBJECTS is created during the installation of Replication Agent. This table contains a row corresponding to each table that is marked for replication. Replication Extract uses the LTMOBJECTS table to identify the data marked for replication.
To capture DB2 data changes, Replication Extract uses the DB2 IFI API to retrieve log records that may originate in the DB2 active and archive logs for inserts, updates, and deletes on tables marked for replication in LTMOBJECTS.
Replication Extract formats the extracted changes, stores the changes in multiple large buffers, then continues to read the DB2 logs.
A separate thread (LTMOC) running in the Replication Agent Address space waits for buffers to fill before transmitting buffers to the Replication Server. This allows the Log Extract and the LTMOC thread to be tuned separately, depending on z/OS, DB2, or network activity.
Replication Extract and LTM for MVS run simultaneously within a single MVS address space as an LTM for MVS started task, continuously reading the DB2 logs.
Replicating transactions from multiple DB2 subsystems can be accomplished in two ways:
Use one Replication Agent started task for each DB2 subsystem.
Use multiple members of a data-sharing group with a single Replication Agent.
With the first option, each Replication Agent started task processes the log of a single DB2 subsystem.
With the second option, all logs are processed by DB2 and records are passed to the Replication Agent as if there were only one log.
