
3-42 IBM Informix OnLine Database Server Administrator’s Guide
If the Logical Log Backup Cannot Complete
OnLine cannot freethis log. Todo so wouldpermitnew recordstooverwrite
the most recent record in the logical log that designates a time when both
physical and logical consistency was ensured. If this happened, OnLine
would be unable to execute fast recovery. (Refer to page 4-39.)
Therefore, this log file maintains a backed-up status until a new checkpoint
record is written to the current logical log file. If you are logged in as user
informix, you can force a checkpoint by requesting the DB-Monitor Force-
Ckpt option. You can also force a checkpoint from the command line by
executing tbmode -c. (Refer to page 7-67.)
If the Logical Log Backup Cannot Complete
If a failureoccurs whileOnLine isbacking upa logicallog file,it handlesthe
situation in the following manner.
During a restore, you can roll forward anylog files that were already backed
up totape before the failure. Thepartial log remains onthe tape as well. The
logical log file on disk that was in the process of being backed up at the time
of the failure is not marked as backed up.
If a logical log backup fails, the next logical log backup session begins with
the logical log file that was being backed up when the failure occurred.
Even if the failure was so severe as to require an immediate restore, the
restore procedure provides you with the opportunity to back up to tape any
logical log files on disk that are not marked as backed up.
Hereis an example.A logical logfile isbeing backed upand a failure occurs.
The backupis interrupted. A restore isneeded. Howdoes therestore handle
the partial backup on tape?
Callthistape,whichcontainsbothvalidbacked-up log filesandapartiallog,
Tape A.
When the restore procedure begins, OnLine reads the appropriate archive
tapes. After readingand restoring the archivetapes, OnLinepromptsfor the
first logical log file since the last archive. Assume that log file is the first log
file on Tape A. The operator mounts Tape A.
OnLinereadseachlogical log fileinsequence.WhenOnLine reachesthe end
of the firstlog file, itrollsforwardallthe operationsdescribedby the records
contained in that file.
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