Re: Why is "shutdown abort", then backup bad

cs charlie wrote:
> One of our database is using "shutdown abort", and then take a cold backup.
> Users on metalink are strongly against it.
>
> If we take a cold backup, everything we need to do a instance recovery is in
> online redo logs. If people can use "shutdown abort" and startup again
> during normal database administration, why can not we use COLD backup of
> "shutdown abort"? It is just do a instance recovery now or do a instance
> recovery in the future.

One reason is that in the future, everything might not be put back in the exact same place, and then there would be stuff lost. If you do a proper shutdown or hot or rman backup, then you don't have to worry about the redo logs, which are generally the weak link in Oracle's way of doing things.

Another reason is the "fractured block" issue. Since Oracle blocks are a multiple of OS blocks, it is possible that the first part of the Oracle block has been written out, while the latter part hasn't yet. In hot backup mode, extra information is written to the redo to fix this, not there when you shutdown abort, and difficult to simulate in testing. So you will eventually get screwed. (rman is smart enough to account for this by retrying the backup of the blocks at issue until they are ok).

Also, in some versions/configurations you can hit bugs. You should develop a habit of doing an abort as a last resort. You should develop a habit of knowing what the heck is going on in the database, anyways. Do you have some problem of a huge rollback happening when you shutdown or startup? aq processes bothering things? Forget to shut off agent?

See http://www.dizwell.com/html/backing_up_redo.html

If you feel you have to do the abort, do a startup restrict then shutdown immediate before you backup. And hope like heck nothing is split.

I would advise upgrading to a supported version and using rman. Anything less deserves a flame.

jg

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