HP NonStop G-Series - Manual (Page 58)

Configuring Automatic Transaction Processing
HP NonStop AutoTMF Software User’s Guide—429952-014
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Record-Level Transactions
Record-Level Transactions
Certain programs use a complex record-locking and record-unlocking sequence such
that at least one record is locked for long periods. NonStop AutoTMF software will not
commit an automatic transaction until a program releases all locks obtained under the
transaction. If the processing contains no point where all locks are released, the
automatic transaction is never committed.
The resulting long-running transaction can cause lock contention, deadlocks, and,
eventually, a unilateral abort when the TMF AutoAbort time limit is reached.
Uncommitted updates could be lost. See the
Unilateral Aborts discussion below.
In such cases, you can configure NonStop AutoTMF software to generate one
automatic transaction for each record lock and to commit each transaction as soon as
the record is unlocked. This approach increases the transactional activity but prevents
the occurrence of long-running transactions without changing the program’s locking
behavior.
This feature is enabled by specifying the RECORDTX attribute on both the file on
which the locks are held and the accessing program. If RECORDTX is specified on
either the file or the program, but not on both, RECORDTX is ignored.
To implement RECORDTX, NonStop AutoTMF software maintains a table of records
locked and the associated transaction for each lock. If the same record is locked
multiple times, the same transaction is used for each lock until the lock is released and
the transaction is committed.
Exceptions
Certain sequences of operations do not lend themselves to the generation of automatic
transactions for each record lock. In these cases, the RECORDTX attribute is not
supported and cannot be used:
•
If a program issues READLOCK (In COBOL, READ NEXT WITH LOCK) to read
records sequentially, NonStop AutoTMF software cannot predict the key of the next
record that will be locked, so NonStop AutoTMF software cannot identify which
transaction to use if the same record is locked more than once. As long as
READLOCK is used to lock records that are not already locked, READLOCK may
be used with RECORDTX.
•
If a program does a LOCKFILE after locking two or more records, the file cannot
be locked unless the records are unlocked first. Otherwise, the same record could
be locked under more than one transaction, leading to internal deadlocks. If a
LOCKFILE operation that has more than one record lock is requested, the
LOCKFILE operation will be abended.
•
If a program issues READUPDATELOCK with positioning by a unique alternate
key, NonStop AutoTMF software cannot predict the primary key of the record being
locked, so NonStop AutoTMF software cannot identify which transaction to use if
the same record is locked more than once. As long as READUPDATELOCK is