RDF System Management Manual

Network Transactions
HP NonStop RDF System Management Manual—524388-003
13-7
Takeover Phase 3 – Network Undo
Takeover Phase 3 – Network Undo
Note that with RDF/ZLT no undo operations are performed during the network undo
phase because no committed transactions are undone.
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.
Takeover Phase 3 Performance
The speed with which a takeover completes for an entire RDF network varies based on
the number of systems in the network and how far any system had fallen behind when
the takeover was initiated.
For example, if you have three systems in your RDF network, and all extractors on all
three systems were keeping up with audit generation on their systems, and then one
system fails, the takeover operations may only take a modest number of additional
seconds to complete phase 3 takeover processing.
In contrast, if you have three systems in your RDF network, and one extractor had
fallen 60 minutes behind at the time its system went down, then phase 3 takeover
processing on the other two systems will take many more seconds to complete. The
reason for this is that phase 3 processing on the two systems that were not behind will