Choosing Automatic Logical-Log Backup (ON-Archive)
Choosing Automatic Logical-Log Backup (ON-Archive)
Use
You can back up the logical log of your Informix database using automatic backup with
ON-Archive . This means starting a logical-log backup at certain times each day with tape as the storage medium.The main problem with automatic backup is that the backup is not started in time and the logical log completely fills. However, Informix and SAP help you solve this problem with the supplied scripts
logevent.sh and arcauto , which automatically detect when a backup is required and then start it. For an overview of these scripts, see SAP Scripts for ON-Archive.Prerequisites
To use automatic logical-log backup, you need to define volume sets and volumes. Refer to
Setting Up Volume Sets and Volumes for ON-Archive with SAP Scripts. The SAP scripts define volume sets and volumes to match the backup scripts described in "Procedure" below.Procedure
The following table summarizes the advantages and disadvantages of automatic backup:
Summary of Automatic Logical-Log Backup
Advantages |
Disadvantages |
Simple Limited operator attention is required Scripts are supplied to facilitate set-up and running DBA Planning Calendar in CCMS of SAP System makes scheduling easy ON-Archive commands need not be entered by hand causing less chance of error |
Logical log fills up if operator forgets to do backup, but scripts reduce this risk Logical log needs lots of disk space to reduce chance of filling up (1 GB recommended, 2 GB overall required due to mirroring) Extreme system crash (both logical log disks fail) immediately before a backup risks losing a lot of work |
The remainder of this process assumes that you choose automatic logical-log backup.
Refer to
Backing Up the Logical Log in the DBA Planning Calendar (Informix).With this approach, you can plan backups regularly, for example, once or twice a day. You must change the tape volume as required. The DBA Planning Calendar calls the script
arcauto at the times that you specify.The logical logs might fill up during very high database workloads when a lot of extra transactions are generated. In this case, consider using the trigger approach (see below) as well for extra security.
With this method, you have to remember to start the backup regularly, for example, at 17:00 each day. However, you risk forgetting to start the backup on time. This might result in the logical log filling up and then the database stops processing. For more information, see
Refer to
Backing Up the Logical Log (Automatic) in the DBA Planning Calendar (Informix).
To install the script, see
Using the trigger approach makes sure that, if there is a heavy workload, the logical-log files are backed up before they fill. You must always make sure that an empty tape volume is in the tape drive, ready for the next backup. For details of the scripts used to trigger the backup, see
SAP Scripts for ON-Archive.You combine the approaches described above to make sure that the logical logs do not fill. SAP strongly recommends this combined approach.
You can also enter your own automatic backup commands on the command line. However,
In general, it makes sense to have a very large logical log (at least 1 GB) with automatic backup, because this reduces the chances of the log completely filling. With very large databases (that is, with more than 1 GB of logging activity per day), consider either creating multiple logical-log backups each day or increasing the size of the logical log even more.
Result
You have decided to use automatic logical-log backup and you have decided which type to use. This is an essential part of deciding your
approach to logical-log backup with ON-Archive .
See also:
Informix documentation at
http://www.informix.com