RMAN Incrementally Updated Backups

In this post I will explore the RMAN Incremental Backups. Incremental backups are used best in Data Warehouse environments where there is a lot of data to backup and keeping multiple copies on the disk takes space.


There are few alternatives Oracle provides to optimize backups of large databases and the incrementally updated backups strategy is one of them. Actually is the Oracle recommended backup policy!

You can NOT use OS methods to take Incremental Backups. Only RMAN will let you take Incremental backups.

The incrementally updated backups allow you to apply database changes incrementally (i.e. every day) to an image copy (not zipped) full backup! That is you update the level 0 full backup with new data incrementally all the time. This way you don't have to keep old full backups, spread over days, separately with their individual archive logs and controlfiles. Even you don't have to take full backups periodically any more! You only take one full backup (level 0) at the beginning and you keep on updating it every day incrementally with the new changes in the database. By applying the changes to the last backup copy, you are bringing the backup copy forward in time. This is also called rolling forward the backup copy.

In my case I used this backup methodology to reduce the ammount of disk space used for backups, as I didn't need to keep and individual full backup of the datawarehouse for each day. I only took one full backup (level 0) at the beginning. And my retention policy was thereafter for 7 days. In this case the retention policy is the duration of time I kept the incremental backups before applying them on the full backup.

To improve the performance of incrementally updated backups another feature called Change Tracking has also been introduced in Oracle 10g. This lets you record the changes in the blocks of datafiles in a separate datafile in the database called Change Tracking File. Then when the time for backup comes, RMAN reads the Change Tracking File to find out the changes which happened to the database instead of scanning whole datafile. This makes the backup much more faster.

So, before running the incrementally updated backup backup script, I enable change tracking in the database like this:

1. First check to see if change tracking is already enabled by querying the DBA view like this:

SQL> conn / as sysdba

Connected

SQL> SELECT STATUS''FILENAME''BYTES FROM V$BLOCK_CHANGE_TRACKING
SQL> /

STATUS''FILENAME''BYTES
--------------------------------------------------------------------------------
DISABLED

2. Then enable Change Tracking.

SQL> alter database enable block change tracking using file '/usr/local/oracle/testdw0/rman_change_track.dbf';

Database altered

The Script I used to take an Incrementally Updated Backup is rman_incr_backup.sh below. This is a sript which uses non-default RMAN location as I explicitly indication where the backups should be stored on disk. This version doesn't use FRA (Flash Recovery Area) either.

# ########################################
# !/bin/bash
# Unix controls
trap cleanup 1 2 3 15
cleanup()
{
echo "Caught CTRL-C Signal ... exiting script."
exit 1
}
# Oracle Variables
export ORACLE_SID=testdw0
export ORACLE_BASE=/usr/local/oracle
export ORACLE_HOME=/usr/local/oracle/product/10.2.0.1
export PATH=$PATH:${ORACLE_HOME}/bin
# RMAN INCREMENTALLY UPDATED BACKUPS (Window of 24 hours)
rman target=/ << EOF
CONFIGURE CONTROLFILE AUTOBACKUP ON;
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '/usr/local/oracle/backups/rman_bkps/dwbacks/atbckp_cntrlfile_testdw0%F';
run {
ALLOCATE CHANNEL RMAN_BACK_CH01 TYPE DISK FORMAT '/usr/local/oracle/backups/rman_bkps/dwbacks/databasefiles_%d_%u_%s_%T';
CROSSCHECK BACKUP;
RECOVER COPY OF DATABASE with TAG 'testdw0_incr_update';
BACKUP INCREMENTAL LEVEL 1 FOR RECOVER OF COPY with TAG 'testdw0_incr_update' DATABASE;
sql 'ALTER SYSTEM ARCHIVE LOG CURRENT';
BACKUP as compressed backupset ARCHIVELOG ALL format '/usr/local/oracle/backups/rman_bkps/dwbacks/archivelogs_%d_%u_%s_%T' DELETE INPUT;
CROSSCHECK BACKUP;
DELETE NOPROMPT OBSOLETE;
DELETE NOPROMPT EXPIRED BACKUP;
RELEASE CHANNEL RMAN_BACK_CH01;
}
EXIT;
EOF
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