Emergency Logical-Log Backup (SAP Library - SAP Database Guide: Informix (BC-DB-INF-DBA))

Emergency Logical-Log Backup

Purpose

This section describes what to do when the logical log of your Informix database is full. The database stops processing when the logical log is full and you must then perform an emergency logical-log backup. This occurs when you have not backed up the logical log in time. When the logical log is backed up, it is marked as free and the database can continue writing transactions to it. For more information about logical-log backup, see Informix Logical-Log Backup.

Reasons why the logical log might fill up include the following:

The logical-log backup has not been started in time.

The current backup tape is full and a new one has not been mounted.

An archive is in progress and you have no more tape drives free to back up the logical log.

In this case, you must choose between either aborting the archive to free the tape drive for the backup or leaving the database suspended until the archive has finished and freed the tape drive.

Prerequisites

You see a message like the following in the message log for the database server:

16:44:49 Logical Log Files are Full - Backup is Needed

The parameter MSGPATH in the ONCONFIG file specifies the name and location of the message log. However, if you use SAPDBA or onstat -m to view the message log, you do not need to know its name or location. Refer to System Information.

Process Flow

Caution

You must use the same tool to do the emergency logical-log backup as you normally use for archives and database and logical-log backups. This is because the data written by ON-Bar , ON-Archive and ontape is not compatible.

ON-Bar

Refer to Performing Emergency Logical-Log Backup (ON-Bar).

ON-Archive

You can take the following approaches to an emergency logical-log backup with ON-Archive :

Use the SAP scripts to help you do the emergency backup.

These automate the process as much as possible. SAP recommends you to use this approach. For more information, see Emergency Backup with ON-Archive using SAP Scripts (ON-Archive).

Perform the emergency backup on your own.

SAP does not recommend you to use this approach. For more information, see Emergency Backup with ON-Archive without SAP Scripts (ON-Archive).

ontape

Refer to Performing Emergency Logical-Log Backup (ontape).

Result

The full logical log is now backed up, allowing the database to continue processing.

Note

After the emergency logical-log backup, SAP strongly recommends that you do a level-0 database backup ( ON-Bar ) or a level-0 archive ( ON-Archive and ontape ) of the database to ensure you do not run into problems using the logical logs that were backed up in this emergency situation. Refer to:

Creation of a Database Backup (ON-Bar)

Creation of an Archive (ON-Archive)

Creation of an Archive (ontape)

To minimize the chances of a full logical log in the future, it is important to make sure that your approach to logical-log backup is correct, so that the logical log is always backed up in time. Refer to:

Approach to Logical-Log Backup (ON-Bar)

Approach to Logical-Log Backup (ON-Archive)

Approach to Logical-Log Backup (ontape)

See also:

Informix documentation

Preventing Emergency Logical-Log Backup