Re: Hot Backups

Jon Goldberg (jgoldberg_at_dbintellect.com) wrote:
>While running hot backups with a tablespace in begin backup mode had
>Oracle crash or shutdown in abort mode?!? When Oracle comes back up it
>requires Media Recovery. To me this is a BUG. Oracle does not have that
>documented. Why should Oracle care since all begin backup does is put a
>rom in the v$ tables and a marker in the redo log.

Jon,

This behavior is described in the Database Administrator's Guide in Chapter 18, "Backing Up a Database":

 "If you forget to indicate the end of an online tablespace   backup and the database is subsequently shut down, ORACLE   assumes that media recovery is necessary at the next   instance startup. Recovery may require the use of the   archived redo log."

and, a bit later:

 "If the instance crashes during online backup and the online   log file that was written at BEGIN BACKUP time is reused,   then archived redo log files are required for recovery."

This might not be quite as clear as it should be, so here is some additional info courtesy of one of the RDBMS developers.

ALTER...BEGIN BACKUP sets an indicator in each database file (which then gets written to the backup copy) so that warmstart processing can detect a restored hot backup. The indicator is reset when ALTER END BACKUP is issued. If Oracle crashes before the END BACKUP is issued then a subsequent warmstart sees the indicator and believes that you have restored a hot backup, hence recovery is required.

You can minimize operational difficulty in this situation by doing STARTUP RECOVER after a crash during a hot backup. Crash recovery won't require any archived redo logs if redo logging hasn't wrapped around to the log that was current when BEGIN BACKUP was issued.

As someone else mentioned, either 7.2 or 7.3 (sorry, not sure which) adds a command that can be issued before MOUNT that will reset the hot backup indicator and prevent unnecessary recovery processing when starting up after a crash during hot backup.

/b

--
Bill Manry  -  Mainframe and Integration Technologies  -  Oracle Corporation
Standard disclaimer applies.