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

Network Transactions
HP NonStop RDF/IMP and IMPX System Management Manual—524388-001
13-11
The Effects of Undoing Network Transactions
1. Transaction record locking would have prevented these transactions from altering
the same data.
2. The commit sequence on \M being T
101
followed by T
102
and the commit
sequence on \N being T
102
followed by T
101
unequivocably means that these two
transactions were active at the same time and committed at the same time.
Therefore they could not have altered the same data.
If we return to the issue of T
13
in the example further above, note that the commit
sequence differs on \A and \B. When the purger on \A determines that T
12
, T
14
, and
T
15
must be undone, it also determines that the results of T
13
can be kept intact
because T
13
had to have completed on \B before T
12
. Why? The commit records on
\A guarantee that both T
12
and T
13
did indeed commit. Therefore, although the
commit record for T
12
is missing from \B, the commit record for T
13
is present. This
guarantees that T
13
committed prior to T
12
, and that the results of T
13
can be kept
intact on both nodes.
When a purger determines that it can keep the results of a transaction even though
that transaction follows one that must be undone because data for it is missing
elsewhere, the purger logs an RDF 823 event message identifying the particular
transaction.
Note. If you have local transactions that do not touch data involved in network transaction
activity, and you do not want these local transactions undone just because data might be
missing for the network transactions during a takeover operation, you are advised to configure
separate RDF subsystems: one to protect just the data involved in network transaction activity,
and the second to protect the non-network data. Of course, both sets of data must have no
dependencies on the other.