Re: Help! Backup & Recovery in Oracle8 enterprise edition

TAD wrote:
>
> For simple backup purposes, wouldn't an export be a good idea. We do not
> require the database to go back to say 1:35 am last wednesday. Our
> requirement is simply to restore the database back to what it was on
> Thursday morning. Our system is not usually used at night so we can safely
> shut it down.

If you are willing, as you have indicated, to throw away the entire day's transactions in the event of a failure, then a noarchivelog mode database is fine. For such a situation, however, a cold backup is better than an export. The main reasons are that an export-based recovery strategy is unnecessarily complex, and takes much longer to perform. Cold backups on the other hand are more or less foolproof. Consider the work necessary to restore the database for each backup method:

Restore to a clean host from export:
1. Install Oracle software
2. Install installation-specific configuration files: init<sid>.ora, listener.ora, sqlnet.ora, tnsnames.ora, etc. Hope you saved them somewhere.
3. Mount the instance and create a new database. Hope you saved a trace controlfile or database creat script somewhere. 4. Begin the full import. All actions restoring objects are performed through DDL and DML, one at a time. They cannot be in parallel, they require many operations to complete. Cross your fingers and hope there are no failures.

Restore to a clean host from a cold backup: 1. Install Oracle software
2. Install installation-specific configuration files: init<sid>.ora, listener.ora, sqlnet.ora, tnsnames.ora, etc. Hope you saved them somewhere.
3. Copy backed-up files into place. Resore is performed by simple file copy. Many copies can be performed in parallel, and require few inexpensive operations to complete.
4. (optional) Roll forward to any point in time using redologs.

> Wouldn't an export be better in this case.

Why would it? Are there any redeeming features to an export for the purposes of recovery?

> BTW, what is a "read-consistency failure".

"ORA-1555: Snapshot too old. Rollback segment ... too small." This message occurs when a query cannot obtain a consistent read of a block because it has been overwritten in the rollback segments. It often happens to people trying to perform export-based backups on active systems of any considerable size. It has been covered in many previos threads, so a search on deja.com should turn up a wealth of information on it if you are interested.

--
Jeremiah Received on Tue Dec 14 1999 - 12:30:28 CST