Transaction Windowing

To minimize loss of transactions due to network failure, hardware failure, or any system failure, transaction windowing has been implemented. This means that when a transaction is copied to a physical tape or virtual tape link, it is not immediately removed from the update queue. A certain number of transactions remain in the update queue, called the transaction window.

For example, when global transaction number 500 is copied to tape, it remains in the update queue until transaction number 750 is copied to tape. If a system failure occurs before transaction 750 is copied to tape, transaction 500 still is in the update queue, and is resent in the next dequeue session.

===== TRANSACTION LOGGING STATUS======== Current Number of QUEUE ENTRIES: 250

Current Number of UNPROCESSED QUEUE ENTRIES: 0

Current GLOBAL TRANSACTION NUMBER: 954

Frames in use by TRANSACTION LOGGING: 11

"UPDATE LOGGING" is: ACTIVE

======= "TRANSACTION PROCESSOR"===========

Transaction Processor STATUS: ACTIVE on Process 11

SESSION TRANSACTION *-- ENQUEUED AT --*

NUMBER NUMBER DATE TIME

------- -------- ------- --------

"LATEST" 2 END: 954 11/08/99 14:28:22

BEGIN: 230 11/08/99 14:27:27

"PREVIOUS" 1 END: 479 11/08/99 14:27:28

BEGIN: 1 11/08/99 14:27:16

===============================================

In this example, there are 250 transactions in the update queue, but 0 unprocessed queue entries. The 250 transactions in the update queue are the transaction window entries. These entries have already been dequeued to tape, but have not yet been removed from the update queue. If a system failure were to occur at this point, these entries would be re-sent in the next dequeue session.

NOTE

The lower portion of the output that transactions 1 through 479 were dequeued in the previous transaction logging session. Transactions 230 through 954 have been dequeued in the current transaction logging session. This shows that transactions 230 through 479 were dequeued in both sessions. Again, this is the transaction window.