RDF/IMP, IMPX, and ZLT System Management Manual

Network Transactions
HP NonStop RDF/IMP, IMPX, and ZLT System Management Manual—524388-002
13-6
RDF Takeovers Within a Network Environment
RDF Takeovers Within a Network Environment
If you have configured an RDF network and must initiate a takeover on a backup
system in the network, then you must execute a takeover on all the backup systems in
the network. You do that by issuing an RDFCOM TAKEOVER command on each
individual backup system. When a takeover occurs within an RDF network, each
subsystem’s takeover operation consists of three phases of operation:
1. A local undo phase
2. A file undo phase
3. A network undo phase
Takeover Phase 1 – Local Undo
This phase is identical to a normal RDF takeover (one that is totally unrelated to an
RDF network). It consists of determining what transaction data has already been
applied to the backup database but whose outcomes are unknown. Once the
transactions have been identified, all updates associated with them are undone. The
purger process determines what transactions must be undone and it writes the list into
the ZTXUNDO file in the MIT.
For example, suppose you began a transaction on your primary system, you executed
ten updates, and you committed the transaction, but the extractor process was only
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