RDF/IMP and IMPX System Management Manual (RDF 1.4+)

Network Transactions
HP NonStop RDF/IMP and IMPX System Management Manual—524388-001
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Takeover Phase 2 – File Undo
able to transmit the first five updates to the backup system before being terminated by
an unplanned outage. In such a case, the RDF subsystem recognizes it is missing
data for the particular transaction (because it does not know how the transaction
ended), and it undoes the five updates it had previously applied to the backup
database.
In summary, phase 1 of a takeover operation undoes data associated with transactions
whose complete data did not make it to the backup system at the time the primary
system failed.
Takeover Phase 2 – File Undo
This undo phase only gets executed if volumes went down on the primary system,
transactions were aborted, and the volumes were never reenabled on the primary
system before the primary system was lost. In that situation, RDF determines what
Backout could not undo, and runs the undo.
Takeover Phase 3 – Network Undo
Phase three determines if network transaction data is missing from any of the backup
systems in the RDF network, and marks those transactions to be undone on all of the
systems. For example, suppose you began a network transaction, updated tables on
ten different systems, and then committed the transaction. Now suppose that nine of
the ten systems were able to transmit their updates and commit records to their backup
systems, but the tenth primary system went down before its extractor was able to do
so. Phase three determines that the particular transaction involved all 10 databases,
that one of the backup databases is missing audit data for that transaction, and
identifies the transaction as one that must be undone on the other nine systems (it is
undone during phase 1 on the tenth system). All of the updaters then look for audit
data associated with the transaction, and undo it.
More specifically, each purger process has three phases of work to do:
1. produce the local undo list in the ZTXUNDO file
2. produce the file undo list, if required
3. produce the network undo list in the ZNETUNDO file
The purger of the network master determines what network transactions are
incomplete across the different backup systems, and it produces the master network
undo list. Each purger then uses this master list to ascertain the transaction data that
must be undone on its backup database. For example, if a network transaction
involved only four of the ten primary systems in an RDF network, then that transaction
only needs to be undone on the backup databases where that data was replicated.
Because the other systems were not involved, the transaction does not need to be
listed there. The list of network transactions that need to be undone on a specific
system resides in its ZNETUNDO file.