Thanks for the question, krishna.

Asked: January 24, 2017 - 5:53 am UTC

Last updated: January 24, 2017 - 9:27 am UTC

Version: 11.2.0.4

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Hi Tom,

I knw he snapshot control file is a copy of a database control file and RMAN creates the snapshot control file so that it has a consistent version of a control file to use when either re synchronizing the recovery catalog or backing up the control file.

Can you clarify below questions.

1)Why we need snapshot controlfile and how we made resync catalog without snapshot controlfile in lower versions.

2)When snapshot control file get created

3)In case of failure can we make use of snapshot controlfile to restore database from past backup?

and Connor said...

1) Before snapshots, we would lock the controlfile (you would see CF locks) during the operation that needed a read consistent view. So the snapshot controlfile gives a more scalable solution.

2) It used to be only for rman sync operations (sync with catalog). Now, when we take a normal controlfile backup, we do a snapshot controlfile, and then take the backup from that.

3) Yes. For example, from MOS note 372996.1, we describe an example where "everything" is lost - one of the options is

"If no controlfile backup available it may be also an option to restore CONTROLFILE from a SNAPSHOT CONTROLFILE if available"

You cannot restore *to* a snapshot controlfile.

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A reader, January 24, 2017 - 6:52 am UTC

Thanks for the great explanation.

January 24, 2017 - 9:27 am UTC

glad we could help

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