RDF/IMP and IMPX System Management Manual (RDF 1.3+)

Network Transactions
Compaq NonStop™ RDF/IMP and IMPX System Management Manual—522204-001
13-5
Normal RDF Processing Within a Network
Environment
Normal RDF Processing Within a Network
Environment
Each RDF subsystem within an RDF network conducts its processing individually, as
though it were not involved in an RDF network. That is, for a given RDF subsystem, the
extractor reads the MAT and sends data to the receiver. The updaters read their data from
their image trails and apply it to their UpdateVolumes. During normal processing, no
RDF subsystem (except the RDFNET process within the network master primary
system) interacts with any other RDF subsystem in the RDF network. Therefore, the
performance of an individual RDF subsystem is unaffected by its inclusion within an
RDF network.
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 two phases of operation:
1. A local undo phase
2. A network undo phase
Takeover Phase One – 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.