TMF Introduction (G06.26+)

Transaction Protection and Database Recovery

HP NonStop TMF Introduction—522414-002

3-9

Backout for Distributed Transactions

For a distributed transaction, loss of communication between participating computer

systems (nodes) can result in transaction backout. If a transaction cannot be

committed on all participating systems, it is backed out on all participating systems.

The transaction is backed out if a communication failure occurs at any point either

before the commit or during the phase 1 (prepare) stage of the commit.

For example, assume that communication between destination and source nodes is

lost before the transaction begins Phase 1 of committing its changes. Each node

affected by the loss of communications aborts the transaction; therefore, the

transaction’s changes are backed out and its locks are released, as illustrated in

Figure 3-4.

Another example is failure during Phase 1 of the commit. Phase 1 is the prepare

stage: the commit for the transaction is issued on the local node, and all participating

transaction managers and resource managers are asked to prepare to commit. Phase

1 may fail because either the communication path with a participating node transaction

manager or resource manager is broken or a participating node replies that it cannot

commit the transaction. When Phase 1 fails, the transaction is aborted and backed out

on all nodes participating in the transaction.

Figure 3-4. Network Backout

Tran-SF1000 at \SANFRAN

Begin transaction.

...

I/O to data at \LONDON

...

End transaction.

Participate in Tran-SF1000

01 Reply message fails

Backs out the

transaction

01 Send prepare message

01 Detects failure

Backs out the

transaction

Tran-SF1000 at \LONDON

Transaction operations that are transparent to the application.

VST116.vsd

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