TMF Introduction (G06.24+)

TMF Overview
HP NonStop Transaction Management Facility (TMF) Introduction—522414-001
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Database Recovery
Transaction Backout
Transaction backout reapplies before-images to database records to undo the effects
of an aborted transaction. If the transaction affects data distributed over a network,
backout occurs independently at each network node. If the transaction is distributed,
backout is managed independently by each participating transaction manager or
resource manager. The result of backing out a transaction is the same as if the
transaction’s changes had never occurred.
Volume Recovery
After most volume or system failures in a NonStop system, volume recovery provides
automatic and relatively quick (usually only a few minutes) database recovery.
Volume recovery ensures that the effects of all committed transactions are applied to
the database files, and that the effects of uncommitted transactions are backed out.
Online Dumps and Audit Dumps
Online dumps are copies of database files that are dumped, or copied, to a secondary
storage medium while the application is running and the database is online. Similarly,
audit dumps are copies of audit trail files that are dumped while the application is
running. The dump destination can be either local or remote.
Online dumps with audit dumps support file recovery, the ability to recover database
files. The online dumps preserve the data as of a particular point in time; the audit
dumps, along with current audit trail files, record the changes made to the data since
that time. To recover the database, TMF restores the dumps to disk and applies
changes from the audit records to the database.
File Recovery
Explicitly initiated by the operator, file recovery recovers database files after a disk
media failure or incorrect program update. It uses online and audit dumps to restore
consistency to damaged files.
During file recovery, TMF first restores the database files affected by the failure, using
online dumps. Then it searches the audit trail for the audit records of all transactions
that changed the database files since the last online dump of these database files,
redoes all changes, and backs out the changes of uncommitted transactions. In this
way, file recovery ensures that the effects of committed transactions are written to the
files and that the effects of aborted transactions are backed out of the files.