Re: Why export is not a good archiving tool
Date: Tue, 18 May 2010 01:48:18 +0000 (UTC)
On Mon, 17 May 2010 15:43:31 -0700, keith.michaels_at_gmail.com wrote:
> I need to know why exporting a database periodically is not a suitable
> method for preserve access to historical data. A customer with 10-20
> year retentions is using this to "preserve access" for compliance
> reasons. I would like to push them towards IBM Optim, Outerbay, Solix,
> etc. but I don't know how to explain the shortcomings of their method.
> Apparently the existing records don't have a nice date field to identify
> old data and leaving it in place doesn't protect it from damage or loss.
As other people will undoubtedly tell you, export is a snapshot tool, not
a backup tool. The difference between a snapshot and a backup is that
backup makes it possible to do a complete recovery of all committed
transactions, up to the point of failure. Snapshot, on the other hand,
allows you to restore the state of the database at the moment that the
snapshot was taken. You can not do recovery from export. That means that
export makes it possible for you to store a logical state of your
database at some important moment, like the end of the financial year.
To recover from a backup, you need the backup itself plus all of the
archived logs from the moment of the backup to the moment of the
recovery. No archive logs means that there is no recovery. You can also
do cold backups, which are taken while the database is shut down, and
which can serve both as a snapshot and a basis for recovery but you still
need all of the archives.
Export, being a logical snapshot tool, allows you to export a single table or schema, which backup does not. Backup knows nothing of tables, indexes or schemas. Backup does data files, it's a physical tool. It's 9:45 PM, I am getting ready to go to bed, this is as much as I can type this late. There are several good books about Oracle backup, all of them written by Robert Freeman. Please, check them out, they are very instructive.