SAP BACKING UP LOG ENTRIES by SridharCh1

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									      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

								
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