2.2.6 Creating a Backup ChainA backup chain is the set of backups consisting of a full backup and all of its successive incremental backups. Tracing back on the parent backups of all incremental backups in the chain eventually leads back to that single, full backup.It is possible to have a “multi-forked” backup chain, which is two or more successive lines of incremental backups, all of which begin with the same, full backup. Thus, within the chain there is a backup that serves as the parent of more than one incremental backup.Since restoration of an incremental backup is dependent upon first restoring the full backup, then all successive incremental backups up to, and including the incremental backup specified by the RESTORE subcommand, it is crucial to note the following:
• The actions of retention policy management are applied to the full backup and all of its successive incremental backups within the chain in an identical manner as if they were one backup. Thus, use of retention policy management does not result in the breakup of a backup chain. See Section 5.2.5 for information on retention policy management of incremental backups.The allow_incremental_backups parameter is set to enabled in the BART configuration file to permit incremental backups on the listed database server:After the database server has been started with WAL archiving enabled to the BART backup catalog, the WAL scanner is started:A series of incremental backups are taken. The first incremental backup specifies the full backup as the parent. Each successive incremental backup then uses the preceding incremental backup as its parent. See Section 5.4.3 for information on the BACKUP subcommand.The following output of the SHOW-BACKUPS subcommand lists the backup chain, which are backups full_1, incr_1-a, incr_1-b, and incr_1-c.Note that for the full backup full_1, the BACKUP PARENT field contains none. For each incremental backup, the BACKUP PARENT field contains the backup identifier or name of its parent backup.A second backup chain is created in the same manner with the BACKUP subcommand. The following shows the addition of the resulting, second backup chain consisting of full backup full_2 and incremental backups incr_2-a and incr_2-b.The following additional incremental backups starting with incr_1-b-1, which designates incr_1-b as the parent, results in the forking from that backup into a second line of backups in the chain consisting of full_1, incr_1-a, incr_1-b, incr_1-b-1, incr_1-b-2, and incr_1-b-3 as shown in the following list:Restoring an incremental backup is done with the RESTORE subcommand and its options in the same manner as for restoring a full backup. Specify the backup identifier or backup name of the incremental backup to be restored as shown by the following:Restoring incremental backup incr_1-b as shown by the preceding example results in the restoration of full backup full_1, then incremental backups incr_1-a and finally, incr_1-b.