TMF Operations and Recovery Guide (G06.26+)

Routine Maintenance
HP NonStop TMF Operations and Recovery Guide—522417-003
2-24
What Happens When a Link is Restored
Homogeneous Transactions
When a communications link goes down, homogeneous distributed transactions in the
active state are automatically aborted both in the parent and in all child nodes.
Homogeneous distributed transactions in the committed or prepared state, however,
cannot change states until the link is restored and the involved TMPs are once again
communicating with one another.
Within a parent node, homogeneous distributed transactions in the committed state
cause no problem because TMF can be restarted. Within a child node, if
homogeneous distributed transactions exist in the prepared state, then TMF cannot be
restarted for transaction processing until the in-doubt transactions are completed. If
the link remains down for an extended time, this could be a problem.
Heterogeneous Transactions
When a communications link goes down, heterogeneous transactions in the active
state are aborted at both the parent and child nodes. Heterogeneous transactions in
the committed or prepared state, however, persist until the link is restored and the
involved transaction managers resolve those transactions.
Within a parent node, heterogeneous distributed transactions in the committed state
cause no problem. For example, suppose that a transaction begun by TMF exports a
transaction branch. If the transaction state at the parent (TMF) node is committed
when the link goes down, TMF can be restarted even if this transaction persists (so
that it can inform its children of the transaction’s outcome). But if TMF imports a
transaction branch and this branch is in the prepared state when the link goes down,
TMF cannot be fully restarted unless the transaction branch is resolved by its parent.
What Happens When a Link is Restored
When a communications link is restored, the normal sequence of events for
homogeneous distributed transactions resumes where it was interrupted. The TMPs
that had lost touch with one another reestablish communication, and exchange
information about distributed transactions that were in progress.
If the link failure occurs when the transaction is in the active state in the parent node
and in the prepared state in a child node, the transaction is automatically aborted in the
parent node. When the link is restored, the child-node TMP finds out that the
transaction was aborted in the parent node, and therefore aborts the transaction in the
child node (maintaining consistency between the two nodes).
If communications cannot be reestablished, you might need to resolve incomplete
transactions. See Controlling Individual Transactions on page 3-21 for more
information.