Re: The meaning of tablespace backup mode

Putting a tablespace in BACKUP mode is not the same as taking that tablespace offline. An offline tablespace is not accessible to anyone. It is offline. It must be put online to be accessible.

A tablespace in BACKUP mode freezes the SCN in the datafile(s) headers. You are then allowed to copy the datafile(s) to perform a hot backup. Changes can still be made to the blocks in the datafile(s). Due to a problem called a "fractured block", if any row in the block changes, the entire block is logged in the online redo logs, not just the affected row. So you can incur lots of online redo log activity when the tablespace is in BACKUP mode.

On recovery, the system uses the frozen SCN and the archived logs and online logs to resolve any inconsistencies in the datafile that was backed up while it was active.

HTH,
Brian

Peter wrote:
>
> When you take a tablespace into backup mode
>
> ALTER TABLESPACE tbs BEGIN BACKUP;
>
> Is this the same as taking it offline?
> If it is still online, then what are the ramifications? Can it still
> be accessed or modified by users?
> The manul is not very clear on this.
>
> Thanks

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