Database Reference
In-Depth Information
To have RMAN delete obsolete archive redo logs, as defined by the archivelog deletion policy, issue the following
command:
RMAN> delete archivelog all;
■
run the
CROSSCHECK
command before running the
DELETE
command. Doing so ensures that rMan is aware of
whether a file is on disk.
Tip
To see whether a retention policy has been set specifically for the archive redo log files, use this command:
RMAN> show archivelog deletion policy;
To clear the archive deletion policy, do this:
RMAN> configure archivelog deletion policy clear;
15. Setting the Degree of Parallelism
You can significantly increase the performance of RMAN backup and restore operations if your database server is
equipped with the hardware to support multiple channels. If your server has multiple CPUs and multiple storage
devices (disks or tape devices), then you can improve performance by enabling multiple backup channels.
If you require better performance from backup and restore operations and have hardware that facilitates parallel
operations, you should enable parallelism and perform tests to determine the optimal degree. If your hardware can
take advantage of parallel RMAN channels, there is little downside to enabling parallelism.
If you have multiple CPUs, but just one storage device location, you can enable multiple channels to write to and
read from one location. For example, if you're backing up to an FRA, you can still take advantage of multiple channels by
enabling parallelism. Suppose you have four CPUs on a server and want to enable a corresponding degree of parallelism:
RMAN> configure device type disk parallelism 4;
You can also write to separate locations in parallel by configuring multiple channels associated with different
mount points; for example,
RMAN> configure device type disk parallelism 4;
RMAN> configure channel 1 device type disk format '/u01/O12C/rman/rman1_%U.bk';
RMAN> configure channel 2 device type disk format '/u02/O12C/rman/rman2_%U.bk';
RMAN> configure channel 3 device type disk format '/u03/O12C/rman/rman3_%U.bk';
RMAN> configure channel 4 device type disk format '/u04/O12C/rman/rman4_%U.bk';
This code configures four channels that write to separate locations on disk. When you configure separate
channels for different locations, make sure you enable the degree of parallelism to match the number of configured
device channels. If you allocate more channels than the specified degree of parallelism, RMAN only writes to the
number of channels specified by the degree of parallelism and ignores the other channels.
If you need to clear the degree of parallelism, you can do so as follows:
RMAN> configure device type disk clear;
Similarly, to clear the channel device types, use the
CLEAR
command. This example clears channel 4:
RMAN> configure channel 4 device type disk clear;
