Developing Good Practice for Logical-Log Backup (SAP Library - SAP Database Guide: Informix (BC-DB-INF-DBA))

Developing Good Practice for Logical-Log Backup

Use

This section discusses guidelines for creating logical-log backups on your Informix database with ON-Bar , ON-Archive or ontape .

Caution

It is very important to back up the logical log on time. Otherwise, if it completely fills, the database stops processing. You then have to perform Emergency Logical-Log Backup.

Different backup approaches offer differing levels of protection against a full logical log. For a summary of measures you can take to avoid this problem, see Preventing Emergency Logical-Log Backup.

Procedure

Make sure that logical-log backup is turned on.

SAP strongly recommends you to run your production database with logical-log backup turned on. Make sure that the LTAPEDEV parameter is not set to /dev/null on UNIX or nul on Windows NT. Refer to Editing the ONCONFIG File for ON-Archive (the information on LTAPEDEV applies to ON-Bar, ON-Archive , and ontape ).

Choose the logical-log backup mode carefully.

In general, continuous is the best kind of logical-log backup, because:

The chance of the logical log filling up is reduced.
You always have the most up-to-date logical-log backup possible.

However, the choice of backup mode depends on the data recovery tool you use:

ON-Bar

Refer to Choosing Continuous or Manual Logical-Log Backup (ON-Bar).

ON-Archive

Refer to Choosing Automatic Logical-Log Backup (ON-Archive) and Choosing Continuous Logical-Log Backup (ON-Archive).

ontape

Refer to Choosing Automatic or Continuous Logical-Log Backup (ontape).

Specify a separate storage device for logical-log backup.

To avoid competition with archives ( ON-Archive or ontape ) or database backups ( ON-Bar ), assign a dedicated tape device for logical-log backup. You must do this if you are using continuous logical-log backup. If you use the same device, there is a chance that the logical-log backup is held up due to contention with the archive or database backup. This might lead to a full logical log, and the database then stops processing.

For more information on tape devices, see:

For ON-Bar , see Configuring ON-Bar and your storage manager documentation.

For ON-Archive , see the DEVICE parameter in Editing the config.arc File for ON-Archive.

For ontape , see the TAPE… and LTAPE… parameters in Configuring ontape.

Use a fast storage device, preferably local

With a slow storage device, the logical-log files might fill up more quickly than they can be backed up. This is more likely to happen with a remote device. The best solution is to use a fast local device (for example, a fast local tape drive).

Watch out for logical-log peaks

Certain activities cause the logical log to fill up rapidly, for example, data conversion. Monitor the logical log closely at such times and do the following:

If you are using continuous logical-log backup, change tapes more often.
If you are not using continuous logical-log backup, run extra backups.

Result

The logical logs are backed up using best practice. Therefore, you can be more sure that, in the event of failure involving data loss, you have a suitable logical-log backup that you can use to quickly restore the database with minimal data loss.

See also:

Informix documentation