Backing Up Log Entries

Use

The redo log entries (log backups) are required to recover the database instance after certain system breakdowns. Redo log entries are where the database system logs all changes that database users make to data.

If the log area was damaged by, for example, a system failure, the database system can only repeat the most recent data changes, which it was not able to write into the data area, with log backups.

If the database system was not able to write the most recent data changes to the data area because of a system breakdown, but the log area was not damaged by the system breakdown, the log backups are not necessary.

In this case, the database system can repeat the data changes using the redo log entries of the log area during restart (see Example: Restart).

Regular log backups are also important for another reason: the database system can only overwrite saved log segments of the log area with new redo log entries.

If the database system cannot write any more redo log entries into the log area (log area is full), the database halts.

You can only continue working once you have executed a log backup. Exception: You have activated overwrite mode for the log area (see Log Settings).

Prerequisites

?      You can only back up redo log entries after the database instance has created at least one complete data backup.

?      You have defined a backup template, see Backup Templates and Data Carriers).

?      The database instance is in the ONLINE or the ADMIN operational state.

?      You cannot start any other backup while an interactive log backup is running.

Exception: when automatic log backup is active, you can perform data backups.

?      Only for Microsoft Windows: if you want to backup to a data carrier on a remote computer, carry out the steps described in Backing Up and Restoring Data with Remote Computers.

Activities

Back up the redo log entries from the log area to data carriers at regular intervals.

You can also back up the redo log entries automatically (Activating and Deactivating Automatic Log Backup).

Executing Log Backups

When you execute a log backup you back up (from the log area to a data carrier) all redo log entries that the database system has written since the last log backup. You can use the Database Manager database tool, or the CCMS (in SAP systems).

You can use a backup template for backing up to a file, or a backup template for backing up to a pipe.

?      When the system backs up to a file, it creates the necessary amount of files one after the other, and then saves an amount of data corresponding to the size of a log segment to each file. The remaining data is saved to the last file.

?      Some restrictions apply to backups to pipes, see Information on Different Types of Data Carriers.

For the procedure, see

Database Manager GUI, Backup Procedures

Database Manager CLI, Backing Up and Restoring Database Instances

Database Administration in CCMS, Scheduling Interactive Log Backups

Activating and Deactivating Automatic Log Backup

Switch on the automatic log backup to back up the redo log entries automatically. If automatic log backup is on, then the database system automatically backs up the redo log entries to backup files.

The database triggers a log backup whenever a log segment is full. You configure the size of the log segment with the general database parameter LOG_SEGMENT_SIZE.

We recommend automatic log backup in particular for database instances in which a large amount of data is changed and therefore a great number of redo log entries is expected.

See

Database Manager GUI, Activating and Deactivating Automatic Log Backup

Database Manager CLI, autolog_on

Database Administration in CCMS, Activating Automatic Log Backup

Archiving Backup Files

For log backups to data carriers of the file type, you have to archive the backup files regularly; see Archiving Backup Files.

See also:

Backing Up and Restoring

Database Administration Tutorial

Activating Automatic Log Backup

Log Backup to a Pipe

Backups with Backup Tools from Other Providers