iX V6.5 (30391-90011)

316 Chapter7

Logging and Recovery

Logical Transactions

transaction A failed to complete, all of its record additions are suppressed. Because

transaction B is dependent upon the suppressed transaction A, it cannot be recovered.

DBRECOV is forced to suppress transaction B, even though it successfully completed during

real-time processing. This potential problem could be avoided if transactions modifying the

database employ locking correctly. Transactions attempting to access the same data

concurrently are serialized by the locking mechanism.

Locking and Transaction Interdependence

To maximize the extent of recovery, locking should be used with logging to eliminate

interdependence of concurrent static and multiple database transactions. Locking by

logical transaction (that is, DBBEGIN and DBEND or DBXBEGIN and DBXEND) guarantees the

logical consistency of the database. For roll-back recovery, locking by logical transaction

ensures that all incomplete transactions are backed out of the database. For roll-forward

recovery, transaction locking is recommended.

Figure 7-2. Suppression of Transactions Due to Inadequate Locking