TMF Introduction (G06.26+)

TMF Overview
HP NonStop TMF Introduction—522414-002
1-9
Transaction Protection
performs an abort operation by backing out all changes the transaction made to
the database.
TMF Transactions Can Be Serialized
TMF protects the transaction from other concurrent transactions so that each
transaction appears to operate alone against the database. It provides this protection
by locking rows or records that might be inserted, updated, or deleted. The locks are
held until the transaction is committed. The locks prevent other transactions from
accessing data affected by uncommitted updates.
The transaction concurrency example in Figure 1-6 illustrates two transactions. Locks
provide concurrency control, and the final balance receives credits from both
transactions, T1 and T2.
Figure 1-6. Serialized Transactions
Denotes record lock for transaction 1 (T1)
Denotes record lock for transaction 2 (T2)
Legend
Reads balance of $50
(with lock)
NEWBAL=$50+$500
END T1
Balance
$50
Balance
$550
CHECKING
Reads balance request
(with lock)
NEWBAL = $550 + $100
•
•
•
•
•
BEGIN T1
Release
BEGIN T2
Access balance of $550
END T2
Writes NEWBAL of $650
Writes NEWBAL of $550
Balance
$650
Release
VST005.vsd