Re: Is an export with consistent=y safe ?

Tommy Raun wrote:

>
> exp consistent=y buffer=300000 file=exp.dmp full=y
>
> However in chapter 23 in Oracle Server Adminstrator's Guide I read the
> following
> sentens:
> "Database exports are not a substitute for operating system backups and
> cannot provide the same complete recovery advantages that the built-in
(snip)
> Why is the export not 'a substitute for the system backup'? Is
> something important missing in the exportfile or is the data not really
> consistent?

consistent=y simply means that the export operation will occur as a "read-only transaction" -- thus, any committed changes made to the database after the start of the export will *not* be included in the export dump file. In other words, the export dump will be logically consistent at the moment the export began. However, that also means that Oracle must maintain a read-consistent view of the database during the export by relying on before images stored in rollback segments -- if there is a lot of update activity during the export, the export could die with a "snapshot too old" error.

The reason the Oracle doc. is saying that an export is not a substitute for an OS backup is that you will need to build a new database in the event of a disk crash in order to have someplace to import the fullk export into (could be very time-consuming) & you will only be able to restore the db at the time of the export -- all subsequent work will be lost.
--

Vincent Ventrone    |  The MITRE Corp.
DBA, Dept. R101     |  M/S C020
vav_at_mitre.org       |  202 Burlington Rd.
(781) 271-7048      |  Bedford, MA 01730