rman.htm
04-06-2002 Bikle
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RMAN

To be completed later.

Most of the 9i RMAN enhancements give a bigger boost to functionality
rather than performance.

We might note a few minor performance related issues.

If memory serves me right, under 8i, if the RCAT is stored solely in
the .ctl file, we could only do full backups; incrementals were not
allowed (I need to check this).

Under 9i, we may run incrementals with a .ctl based RCAT.

Since an incremental requires less CPU and I/O, this could be seen as
a performance boost.

9i offers a new feature named: Block Level Recovery.  

This is a Recovery feature rather than an RMAN feature; I'll list it
here while it's on my mind and then move it later to another section.

Some syntax:
BLOCK RECOVER DATAFILE 9 BLOCK 44;

Obviously if we can restore a few blocks rather than an entire file when we
need only a few blocks, this is a performance enhancement.

Another new 9i recovery feature which might enhance performance in the
right circumstances is 'Trial Recovery'.

This feature tells you if a specific RECOVER command will work or not.

I've run many RECOVER commands in my past which have failed (usually 
during an effort to clone a DB from hot backup).  I am pleased to see
this 'Trial Recovery' feature.  The performance enhancement is obvious;
the feature frees me (in circumstances) from doing multiple restores 
in an effort to search for a checkpoint within a backup.


Another performance enhancement a feature which is triggered via the syntax below:

CONFIGURE BACKUP OPTIMIZATION ON;

The above statement will prevent RMAN from backing up tablespaces which have a
static SCN (aka READ-ONLY tablespaces).  Also it will prevent RMAN from backing
up archivelogs more than once.

The statement below will compare backups listed in the RCAT with actual backups.
If it cannot find actual backups, it will list them as expired in the RCAT:

CROSSCHECK BACKUP;

Keeping the RCAT up to date will help performance in some circumstances.

To be completed later.