Re: Deferred Transaction Recoverability

On Fri, 24 Aug 2001 11:09:41 +0800, Dino Hsu <dino1_at_ms1.hinet.net> wrote:

>rollback segments. I try to summarize here:
>1.Logfiles is more of 'instance recovery'

and recovery from storage media failure, as in lost disk.

>2.Rollback segments is more of 'transaction management'

and transactional recovery. As well as read-consistency.

>3.The reason I was confused is it's nothing wrong to call 'transaction
>management' as 'transaction recovery'. However, they are meant to deal
>with different problems, they can work closely together but should not
>be mixed up.

yes. But both are handled by the rollback segments. redo logs (logfiles) are more for disk failure, although they are used as well to restore the rollbacks to their correct status, so that transactional recovery can take place.

>4.On the next system startup after an instance failure and thus some
>possible manual procedures from administrators, instance recovery
>process is started by SMON, in which logfiles are involved first
>(control files, datafiles, logfiles are 'synchronized'), and datafiles
>and rollback segments later (transaction recovery 'deferred') as is
>also performed in normal times.

You got it in one.

>5.Both for instance recovery and transaction management, SCNs or
>System Change Numbers are used to identify transactions.
>

Ditto.

Glad to be of help. Now, if the subject matter interests you: start reading the backup and recovery manual. If not, leave it to your DBA to worry about. It's a whole world, not much use to you other than the general principles. Unless you're the one stuck with the DBA job.

Cheers
Nuno Souto
nsouto_at_optushome.com.au.nospam Received on Fri Aug 24 2001 - 06:16:24 CDT