How to de-register the database from rman catalog

Hope every one is doing great!!

I have two questions.

1. we have oracle rman catalog db in which all the prod databases are registered, we cloned the database to a different server and by mistake registered the database without changing the DBID to the same catalog. I want to de-register the one which was recently added to the catalog as DBname and DBID are same.

2.How do we investigate in a step wise the performance problem when a query is all of a sudden running slowly. I know there is no standard solution for this problem, but would like to know how we should systematically investigate the problem any notes would work for me.

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Thanks & Regards
Nilesh
Oracle DBA (sqlplus "/as sysdba" is my world)



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