3-42 IBM Informix OnLine Database Server Administrator’s Guide
If the Logical Log Backup Cannot Complete
OnLinecannot free this log. To do so would permit new records to overwrite
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 topage 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 theDB-Monitor Force-
Ckpt option. You can also force a checkpoint from the command line by
executingtbmode -c. (Refer to page 7-67.)
If the Logical Log Backup Cannot CompleteIfa failure occurs while OnLine is backing up a logical log file, it handles the
situation in the following manner.
Duringa restore, you can roll forward any log files that were already backed
upto tape before the failure. The partial log remains on the tape as well. The
logicallog 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
restoreprocedure 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 log file is being backed up and a failure occurs.
Thebackup is interrupted. A restore is needed. How does the restore handle
the partial backup on tape?
Callthis tape, which contains both valid backed-up log files and a partial log,
Tape A.
When the restore procedure begins, OnLine reads the appropriate archive
tapes.After reading and restoring the archive tapes, OnLine prompts for 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.
OnLinereads each logical log file in sequence. When OnLine reaches the end
ofthe first log file, it rolls forward all the operations described by the records
contained in that file.