Who needs DB2’s Incremental Delta Backup?


Marin Komadina

This
article explains how to organize and perform a delta incremental database
backup.

Delta backup will be your IT manager’s best friend, especially
if he is fighting a budget, your DBA will love it because he will learn
something new, and storage guys will complain because they will not get paid as
before.

Delta
backup has been supported since version 7.2 (7.1 Fixpack 3) with a small
surprise:

APAR
IY22633,INCREMENTAL BACKUP MIGHT BE MISSING PAGES, First Fixed in: DB2
V7 FixPak 4.
UDB Version 8
includes several backup and recovery enhancements, but incremental delta backup
functionality remains the same.

This article covers:

  • Backup Terminology
  • Online Backup Classification
  • Database parameters
  • Incremental Delta Backup Example
  • Backup Control

Backup Terminology and Parameters

As a brief refresher, lets review some backup terminology.

  • Backup Type
    • Offline database backup –
      database in deactivated status, log parameters settings for circular logging
      (LOGRETAIN
      = OFF and USEREXIT = OFF), only crash recovery or version recovery possible

    • Online database backup
      – database activated (database files in use), log parameters settings for
      archive logging (LOGRETAIN=ON and USEREXIT=ON), rollforward recovery enabled
  • Logging
    • Circular logging –
      reuse of log files in round robin, content not preserved

    • Archive logging
      – upon commit, log files are closed and become offline archived logs
  • Log file
    • Online
      log file –
      log file with active content in defined database log directory

    • Offline
      log file
      – filled log file, moved from log file path to archive storage
  • Recovery history file

    Special logging repository for tracking various database
    activity: backup, restore, rollforward, alter, rename, quiesce tablespace,
    load, drop, reorganization of table or update of table statistics. Entries from
    this file are read with the LIST HISTORY command.

Online Backup Classification

  • Full online database backup (full)
    • full copy of all database pages
    • standard metadata set (db configuration, table space definitions, db history)
  • Incremental online database backup (cumulative)
    • updated database pages since last successful full backup
    • standard metadata set (db configuration, table space definitions, db history)
    • full copy of changed LOB and LF data types from previous full, incremental or delta backup

      incremental backups

  • Incremental Delta online database backup (incremental)

    • updated db pages since last successful full, incremental or incremental delta backup
    • standard metadata set (db configuration, table space definitions, db history)
    • full copy of changed LOB and LF data types from previous full, incremental or incremental delta backup

Database Parameters

The
main parameters for controlling backup behavior are:

  • Track modified pages
    TRACKMOD=ON – enable Incremental-/Delta-Backup by starting tracking database updates

    TRACKMOD=OFF – disable Incremental-/Delta-Backup

    (database
    version < V7.2 default: TRACKMOD=NO, database version >= V7.2
    default: TRACKMOD=YES)

  • Log retain for recovery

    LOGRETAIN=ON – enable archive logging

    LOGRETAIN=OFF – enable circular logging

  • User exit for logging

    USEREXIT=ON
    – The userexit parameter causes the database manager to call a user exit
    program for archiving and retrieving database logs. This parameter allows
    roll-forward recovery and automatically enables logretain to be active.

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