TurboIMAGE/XL Database Management System Reference Manual (30391-90012)

670 AppendixG
Recovery and Logging Quick Reference
Recovery Quick Reference
Intrinsic Level Recovery (ILR)
• Should only be used to force flushing to disk after a call to DBPUT or DBDELETE.
• Not required with TurboIMAGE/XL, because physical integrity is automatic and
transparent to the user. The same physical integrity is available through Transaction
Management (XM) on MPE/iX without enabling ILR. Using XM instead of ILR requires
less overhead.
• Guarantees that at most one DBPUT and DBDELETE call per process will be lost. The
database is recovered automatically if recovery is needed the next time the system is
rebooted.
• Cannot use deferred output (AUTODEFER). This ensures the structural integrity of the
database.
• Cannot defer writing modifications to the database because deferred output cannot be
used.
• Is intrinsic driven; transaction locking is not necessary.
• Incurs some overhead on DBPUTs and DBDELETEs due to the request to flush
Transaction Management (XM) log file pages to disk at the end of each completed
DBPUT and DBDELETE.
• Can be used with user logging.
Roll-Forward Recovery
• Provides recovery of a database, both structurally and logically, to a likeness of its state
at the time of a hard system failure.
• Uses DBSTORE and DBRESTOR or TurboSTORE/iX 7x24 True-Online Backup (with
ONLINE=START or ONLINE=END option) to backup the database and MPE/iX RESTORE
command to restore the database to a consistent state.
• If True-Online Backup was not used to store the database, and the AUTO option is in
use, all logfiles in the logging cycle must be present for recovery. All logfiles starting
with the first one,
XXXXX 001, are required regardless of some intermediate recovery or
use of the STOP/RESTART feature.
• Requires logging be enabled. During recovery all log files since the last database backup
copy must be applied.
• TurboIMAGE/XL logging depends upon exact correspondence between the stored
backup database copy and the working database on disk at the time logging was
interrupted. The DBSTORE flag and log file time stamp will enforce this condition.
• Logging provides recovery of both intrinsics and transactions following a system failure.
• Is initiated with the >RECOVER command of DBRECOV. The database must be purged
and restored before recovery is initiated.
• During a start recovery operation all transactions in the memory buffer will be lost.
• Does not require logical transaction locking; however, it is recommended.