IBM 000-8697 Manual Do Utilizador

IBM Informix OnLine Database Server Administrator’s Guide

If you modify the initial configuration values, you might be able to improve
performance. Weigh these three considerations:

■

Size the logical log large enough to prevent a long transaction
condition. (Refer to

 for a definition of a long transaction.)

■

Create enough logical log files so that you can switch log files if
needed without running out of free logical logs.

■

If your tape device is slow, ensure that the logical log is small enough
to be backed up in a timely fashion.

Refer to

for a detailed discussion of the factors that affect the rate

at which the logical log files fill.

The

LTAPEDEV

 configuration parameter specifies the logical log backup

device. The value you choose for

LTAPEDEV

 has the following implications:

■

If the logical log device differs from the archive device, you can plan
your backups without considering the competing needs of the
archive schedule.

■

If you specify /dev/null as the logical log backup device, you avoid
having to mount and maintain backup tapes. However, you can only
recover OnLine data up to the point of your most-recent archive tape.
You cannot restore work done since the archive.

■

You can specify a logical log backup device attached to another host
system and perform backups across your network.

Look at the copy of your configuration file and compare the values specified
by

LTAPEDEV

 and

TAPEDEV

.

LTAPEDEV

 is the logical log tape device.

TAPEDEV

 is the archive tape device.

Ideally,

LTAPEDEV

and

TAPEDEV

each specify a different device. When this is

the case, you can invoke the Continuous-Backup option to automatically
copy the logical log files to tape as they fill. The archive schedule is irrelevant.