AutoTMF Software User's Guide (Update 11)

Usage Guidelines

HP NonStop AutoTMF Software User’s Guide—429952-013

5-8

NonStop AutoTMF and Process Pairs

If AutoTMF is used, no error 75 occurs on a takeover because AutoTMF creates new

automatic transactions in the backup process to access audited files.

However, when a primary process fails, automatic transactions may or may not have

been aborted, depending on the cause of the failure.

If the failure is due to a programming error, such as a trap or a call to STOP or ABEND,

AutoTMF commits all outstanding transactions before the program stops.

If the failure is due to an environmental error, such as the loss of a CPU, then the

active transactions are unilaterally aborted.

After the primary process failure, the backup process takes over at some point in the

processing, without knowing if all the previous updates have been committed.

In theory this situation could be remedied by making AutoTMF commit all active

transactions whenever the primary process does a CHECKPOINT to the backup

process. However, to commit transactions at every checkpoint would require that no

record locks or file locks be held by the program when it calls CHECKPOINT. If the

program still held locks, AutoTMF would have to abend the process after committing

the transaction.

How to Use AutoTMF with Process Pairs

In T0581AAJ, AutoTMF was enhanced to intercept the CHECKMONITOR procedure

and insure that the backup process of a process pair always initializes the AutoTMF

internal segment upon startup to insure the AutoTMF environment in the backup

process is ready in the event of a takeover.

However, be aware that

•

No reliable way exists to checkpoint transactions.

•

In some cases, a CPU failure may cause the database updates to be rolled back.

When the backup process takes over, AutoTMF starts generating new automatic

transactions without knowledge of the transactions that occurred in the failed primary

process. The backup process behaves as if the work had been completed and does

not reapply an update that was rolled back.

Recommendation

To limit the scope of the recovery required in the backup process, you should set the

ATMFProgram attribute MAXUPDATES be set to 1.Setting MAXUPDATES to 1 forces

AutoTMF to commit transactions immediately after an update. Then if a failure occurs,

at most one update must be recovered by the backup process.