Is there a way to manually clear UndoTablespace?

Is there a way to manually clear UndoTablespace.

For our Prod DB we take daily backup using Data Pump. Schema size is around 120GB.  Backup takes more than 12hrs to complete. We noticed that whenever we restart the DB and then run the backup it complete merely in 1.5 or 2hrs.

I suspect it might be due to uncommitted transactions which might be there in undotablespace and after restart it gets clear, which results in speed up the backup.

Could anyone please let me know what could be causing the issue.
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johnsoneSenior Oracle DBACommented:
What you are talking about is read consistency.  From the time the select statement that datapump is using starts to the time it completes you get the same view of the table that you are selecting from.  So, if the select statement takes 10 minutes, and 5 minutes into it a user updates and commits a change, the select will see the previous version of the row.

The only uncommitted transactions that would interfere with read consistency are ones that have been written to disk and you should only see this on a really active database.

Datapump is not a backup.  It is a method to copy data, but really shouldn't be considered a viable backup.  It cannot be rolled forward.  If you are OK with losing data then it can be viable, but I would only use it if the database was started with STARTUP RESTRICT so that no users could be doing anything while it was running.  You have a better chance for consistency that way.

FYI - you cannot force undo to be marked as unneeded or "flush" it.
slightwv (䄆 Netminder) Commented:
Remember from your previous questions but I have to state it again:  Export is not a backup.

To answer the first question:  I do not know of any way to 'purge' the undo short of a shutdown immediate.  Even if there was, it would be fairly dangerous to do and would likely result in some data issues.

Are there a lot of users on when you run your export?  It might not be uncommitted transactions.  Instead it might be committed ones.  If the export is trying to be consistent and a lot of DML happens while the export runs, it will have to go to the redo to grab the older blocks.
cloudtechnicianAuthor Commented:
slightwv, we'll be implementing RMAN backup in few months. I understand it's the only reliable and recommended way to take backups.

Are there a lot of users on when you run your export?  
No there are not many users when the script execute and perform export.

The only confusion is why does backup complete in 2hours(within maintenance window) after restarting DB which otherwise takes more than a day time.
slightwv (䄆 Netminder) Commented:
Not sure why it only takes two hours after a restart.

Are you just talking about just the export time or the complete end to end process?

I cannot think of anything in a newly started database that would affect export in such a way over one that has been running.

I'm pretty sure it isn't anything in UNDO.

I would look at what system resources are maxing out between the two different runs.  That should help narrow down where to look.  My gut feeling is memory not disk io.  See if you are swapping to disk.  That will slow things down to a crawl!!

>>I understand it's the only reliable and recommended

To clarify:  It is not the "only" way.  It is the recommended way.

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