TurboIMAGE/XL Database Management System Reference Manual MPE/iX V6.5 (30391-90011)

Appendix H 675
TurboIMAGE/XL versus TurboIMAGE/V
Intrinsic Level Recovery
Intrinsic Level Recovery
Intrinsic Level Recovery (ILR) is not required to protect the structural integrity of the
database, because in default recovery mode TurboIMAGE/XL takes advantage of an
internal MPE/iX file system service, called Transaction Management (XM), to provide
intrinsic level backup and recovery. Unless AUTODEFER is enabled, all intrinsics that
modify the database (DBPUTs, DBDELETEs, and DBUPDATEs) are written to XM log file pages
by MPE/iX. In default recovery mode, XM log file pages are only written to disk when one
of the following occurs:
• A system-specified time has elapsed.
• A request is made by a subsystem, such as TurboIMAGE/XL, to flush the XM log file to
disk (for example, ILR is enabled, or DBEND mode 2 is specified and logging is enabled).
• The XM buffer is full.
Thus, intrinsics that have completed may not yet be written to disk. If a system failure
occurs, only intrinsics that have been written to disk are recovered.
When recovery is
necessary, it must be performed at system startup time before anyone
modifies the database.
ILR also uses the MPE/iX Transaction Management service. When ILR is enabled, XM log
file pages are written to disk at the end of each completed DBDELETE and DBPUT. If a system
failure occurs, at most only one DBPUT or DBDELETE is not recovered. (Note that a completed
DBUPDATE does not force a XM log write to disk.) Because of these differences in
implementation, ILR on TurboIMAGE/V is not completely compatible with ILR on
TurboIMAGE/XL.
ILR does have performance implications. Therefore, you may wish to reevaluate your use
of ILR with TurboIMAGE/XL. ILR is no longer necessary to ensure the structural integrity
of the database. However, if your data is not easily recoverable (information taken over the
telephone, for example) you may wish to use ILR because at most only one intrinsic can be
lost.
NOTE Before moving TurboIMAGE/V databases to MPE/iX, it is recommended that
ILR be disabled. If it is not, TurboIMAGE/XL assumes you want ILR to
remain enabled.
Major Differences
• ILR is performed by MPE/iX Transaction Management. As a result, the ILR file
DatabaseName00 does not exist. All transactions are logged to the MPE/iX Transaction
Management log file.
• ILR is not required to protect the structural integrity of the database.
• ILR is not required for roll-back recovery.
• DBUPDATE is included with DBPUT and DBDELETE in Intrinsic Level Recovery. However,
completed DBUPDATEs are not guaranteed to be committed to the log file for recovery.