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Re: Export every day

From: Richard Foote <>
Date: Tue, 16 Jul 2002 19:58:06 +1000
Message-ID: <Z%RY8.36046$>

Hi Peter,

How long is a piece of string (not very original but I couldn't think of a single metaphor that didn't include David Bowie :)

How much rollback space you need for a consistent=y export to work is dependently entirely on how much change activity is occurring in your DB at the time. Remember, the point of consistent =y is to allow the export to see the value of all data at the point of time the export begins. Therefore is you are doing no or very minimal changes then you can get away with tiny (few) rollback segments. If you are doing a towering mountain worth of changes, you are going to need huge (many) rollback segments. You haven't specified your change activity therefore it is impossible to give you a quantitative answer.

In relation to your other question regarding export and backups. Exports should *not* be considered a genuine method of backing up your database. Yes, it can be a convenient method of restore a lost table and the such but the problem is that you will *lose* data by adopting this backup technique (eg. restoring a lost table will only restore the table from the point of time of the export, all subsequent changes would be lost).

The method you *must* consider in order to perform a valid backup of your DB is to perform O/S copies of the database files. These backups can either be cold (offline) or hot (online) depending on your organisation's requirements but only by doing so can you guarantee the *full* protection of your database.

As I've stated many times, the three things you need to fully protect a database are:

  1. A complete, non corrupt backup of your DB (specifically the data files and control files)
  2. All redo logs from your oldest backup file to the current online redo log (for which an archivelog DB is essential)
  3. A DBA who knows what they are doing.

An export of your DB can be useful in certain circumstances, and might be required and conducted as part of an incomplete recovery scenario but is not a basis of a valid backup strategy in it's own right.

Hope this all helps. If you need any clarification, just let me know.

Good Luck


<> wrote in message news:ah0onm$t62$
> Howard J. Rogers <> wrote:
> > So, CONSISTENT=N is usually OK, but CONSISTENT=Y is available, but
> > lots of rollback space to be in use by the transactions taking place on
> > database during the export.
> How much is "lots"? Lets say I have a 1G db and a 1GHz Pentium 4 with 2G
> -- how much should rollback space I should have to export my data safely?
> Is running exp the preferred way of backing up my data in Oracle or are
> there some other methods I should consider?
> Regards,
> Peter
Received on Tue Jul 16 2002 - 04:58:06 CDT

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