Using the RMAN Recovery Catalog - OCP: Oracle Database 12c Administrator Certified Professional - page 170

■ RC_BACKUP_ARCHIVELOG_SUMMARY
■ RC_BACKUP_SET
■ RC_BACKUP_SET_DETAILS
■ RC_BACKUP_SPFILE
Creating the Recovery Catalog User
and Schema Objects
As we mentioned, the recovery catalog is a schema in an existing Oracle Database. This
schema typically will have its own tablespace, where the RMAN recovery catalog schema
data will be stored. Creating the recovery catalog user and schema is fairly easy. You use
the CREATE USER command to create the database user first. You will then need to create
the tablespace that will store the recovery catalog data.
To Use the Recovery Catalog or Not to Use the Recovery Catalog; That is
the Question
Adding components to any system has the potential to inject problems into that system. The
same is true with the recovery catalog. One database shop implemented the Oracle recov-
ery catalog at the same time they started using RMAN (this was using Oracle Database 10 g).
Initially things worked great, but over time, backup performance became slower and
slower. These performance problems were not seen when the recovery catalog was not
in use. In the end, after lots of troubleshooting, they discovered that a couple of queries
being issued against the recovery catalog schema were not tuned well and that these
queries would slow down a great deal as the catalog schema got larger. They opened a
service request with Oracle, and after some time Oracle found the problem and made a
patch available.
The moral of this story, in our minds, is to use the KISS (keep it simple, stupid) principle
when deciding if you need a recovery catalog or not. If you can justify the additional
component because it will provide significant benefit, then by all means use it. Just
understand that it's something else that may well break, and things always break at the
most inopportune times.