Incremental backups greatly reduce the
elapsed time for Oracle backups, but the RMAN incremental backup
mechanisms can be complex.
In Oracle 10g and beyond, you can apply
RMAN incremental backups to data file image copy backups to roll
them forward to a specified point in time. This new
feature provides the following benefits:
By periodically updating image copies of
data files with incremental backups, the updated image copy of
the data file is moved forward to a more recent state (with more
current SCN). This could potentially result in reduced
recovery time.
This use of RMAN incremental backups avoids
performing a full image copy after incremental backups.
The following statement rolls forward an
image copy of data file u01/app/oracle/backup/grid/data01.imgcopy:
RMAN>
recover datafilecopy '/u01/app/oracle/backup/grid/data15.imgcopy';
Or, you can issue this command to perform
the same operation:
RMAN>
RECOVERY COPY OF DATAFILE 15;
When doing RMAN
incremental backups with Oracle RMAN we need a mechanism to
bypass those data blocks which have not changed. In a
typical tablespace, SQL insert activity places new data blocks
(as the tablespace and data file extends) in "hot" areas of the
data file.
To maximize the
efficiency of RMAN incremental backups with block change
tracking, try to use the APPEND hints with inserts or a low
PCTUSED values for tables and indexes to ensure that all new
rows are placed in new blocks. This reduces overhead,
since only new blocks are tracked with the block change tracking
mechanism.
The syntax for
Oracle block level change tracking is simple:
ALTER DATABASE
ENABLE BLOCK CHANGE TRACKING
USING FILE os_file_name;
Also, see my
notes on the different backup
types and the differences between
incremental cumulative and incremental differential backups.
