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

Network Transactions
Compaq NonStop™ RDF/IMP and IMPX System Management Manual—522204-001
13-9
The Effects of Undoing Network Transactions
8. T
13
commit
9. T
14
(non-network transaction)
10. T
15
(network transaction started on \A)
11. T
14
commit
12. T
15
commit
At approximately the same time system \B executes the following:
1. T
10
(network transaction started on \A)
2. T
20
(non-network transaction)
3. T
12
(network transaction started on \A)
4. T
13
(network transaction started on \B)
5. T
21
(non-network transaction)
6. T
22
(non-network transaction)
7. T
36
(network transaction started on \C)
8. T
21
commit
9. T
22
commit
10. T
36
commit
11. T
20
commit
12. T
10
commit
13. T
13
commit
14. T
12
commit
Assume that the primary system \B goes down after having transmitted the commit
record for T
13
to its backup system \Y. At that point \Y has the commits for T
10,
T
13,
T
20
, T
21
, T
22
and T
36
. \Y only has to perform local undo (during which T
12
is undone).
The purger on \X (the network master) determines that the first transaction requiring
network undo is T
12
because that transaction was active on both \A and \B when \B went
down. Therefore, even though T
12
originated on \A and was committed on \A, it must
be undone on \X (the backup system of \A) because it was undone on \Y (the backup
system of \B). This ensures database consistency across both nodes. Note that when the
purger identifies the first network transaction that must be undone during network undo
processing, it logs an RDF 877 event message specifying that transaction.
Besides transaction T
12
, transactions T
14
and T
15
must also be undone on \X because
they followed the commit of T
12
on \A and their database changes could have been
based on the committed outcome of T
12
. If T
14
and T
15
are not also undone, database
consistency could be compromised because their effects on the database might have
been based upon data that was backed out. Note that T
14
is a local transaction, not a
network transaction. Nonetheless, its database changes could have been based on the