iX V6.5 (30391-90011)

Appendix G 659

Recovery and Logging Quick Reference

Recovery Quick Reference

G Recovery and Logging Quick

Reference

Recovery Quick Reference

The following pages offer a very brief outline of the recovery options in TurboIMAGE/XL.

For more information regarding dynamic roll-back recovery, Intrinsic Level Recovery

(ILR), roll-forward recovery and roll-back recovery refer to chapter 7, "Logging and

Recovery," and chapter 8, "Using the Database Utilities."

You should determine which type of recovery to use based on the size of the database,

frequency of system failures, equipment availability, and other considerations.

Dynamic Roll-Back Recovery

• Allows dynamic transactions to be rolled back on-line while other database activity is

occurring. If a system failure occurs, incomplete dynamic transactions will be rolled

back at the ﬁrst call to DBOPEN for the database after the system is restarted.

• Uses DBXBEGIN, DBXEND, and DBXUNDO intrinsics.

• Requires strong locking. Calling DBUNLOCK after a call to DBPUT, DBDELETE or

DBUPDATE within a dynamic transaction will return an error because the call to

DBUNLOCK must occur after the call to DBXEND. If necessary locks are not acquired

before calling DBXBEGIN, covering locks must be used on the intrinsic calls within the

transaction, or the intrinsic will return an error.

• Requires checking of the status condition before proceeding further after a modiﬁcation

using DBPUT, DBDELETE, DBUPDATE, or after DBUNLOCK,orDBCLOSE in mode 2. If an

error is returned indicating the failure of the intrinsic, the choices are:

— Call DBXEND. The successful modiﬁcations completed within this dynamic

transaction will not be rolled back.

— Call DBXUNDO to roll back the entire transaction. Even successful modiﬁcations

completed within this dynamic transaction will be rolled back.

— Continue with the remainder of the dynamic transaction even though this intrinsic

failed. Be very cautious in your design when taking this option as the ﬁnal result can

be unpredictable.

• Cannot use deferred output (AUTODEFER). This ensures the structural integrity of the

database.

• Can use user logging for roll-forward recovery purposes in the event of a disk media

failure.

• Can be used with remote databases.