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

Network Transactions
Compaq NonStop™ RDF/IMP and IMPX System Management Manual—522204-001
13-7
Communication Failures During Phase Two
Takeover Processing
Communication Failures During Phase Two Takeover Processing
If one RDF subsystem is unable to reach the backup system of another RDF subsytem
during phase 2 processing, phase 2 processing stalls until the communication line comes
back up. This can lengthen the overall duration of takeover operations on all backup
systems. Should this type of stall occur, the RDF subsystem issues an event message
alerting operators to the situation.
Takeover Delays and Purger Restarts
During phase 2 purger work, the network master needs information from the other
purger processes in the RDF network, and, during the latter part of phase 2 processing,
the non network master purgers need information from the purger of the network master.
When a purger process is waiting for information from another purger, it waits for up to
60 seconds, during which time it does not respond to certain requests (such as STATUS
RDF). After a purger has waited 60 seconds, it quits the operation and restarts. This
allows the purger to read the $RECEIVE file, respond to messages that have been
waiting for replies, and then retry phase 2 processing.
Takeover Restartability
As has always been the case, the RDFCOM TAKEOVER command is restartable.
Therefore, if a takeover operation terminates prematurely for any reason on any system
in an RDF network, it can be restarted.
Takeover and File Recovery
When a takeover operation completes in an RDF network environment, the purger logs
two events: one reports a safe MAT position (indicating that all committed data up to
that location was successfully applied to the backup database), and the second (888 or
858) reports whether or not a File Recovery position is available for use on the primary
system. The RDF event 888 reports that a File Recovery is available and it includes the
exact sno and rba to be used for a File Recovery operation on the primary system. If,
however, “kept-commits” have been encountered during phase 2 processing, a File
Recovery position is not available; this is reported in RDF event 858.
If an RDF event 888 is reported, then the specified File Recovery position is based on
both phase 1 and phase 2 processing. Each system logs its own File Recovery position.
While that position may differ from one backup system to the next, the logged position
for any single system is correct. If you supply the returned File Recovery position to the
TMF file recovery process on the primary system, the process recovers the files on the
primary database up to that point. If you use File Recovery to a MAT position on all
primary systems in the RDF network, in each case using the returned File Recovery
positions, then your primary distributed database will be consistent across the RDF
network.
You would use the File Recovery position with File Recovery in situations such as the
following. Assume you have had an outage of your primary system, you have executed
the RDF takeover operation on your backup system, and you have resumed business
transactions on your backup system. Assume further that the former primary system has
been repaired, it is back online, and you want to switch your business transactions from