IBM 000-8697 Manual Do Utilizador

IBM Informix OnLine Database Server Administrator’s Guide

OnLine cannot 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 to

.)

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-M

onitor Force-

Ckpt option. You can also force a checkpoint from the command line by
executing tbmode -c. (Refer to

.)

If a failure occurs while OnLine is backing up a logical log file, it handles the
situation in the following manner.

During a restore, you can roll forward any log files that were already backed
up to tape before the failure. The partial log remains on the 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.

Here is an example. A logical log file is being backed up and a failure occurs.
The backup is interrupted. A restore is needed. How does the restore handle
the partial backup on tape?

Call this 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.

OnLine reads each logical log file in sequence. When OnLine reaches the end
of the first log file, it rolls forward all the operations described by the records
contained in that file.