Re: Question on REDO & SCN

Thanks a lot Jonathan

-Pradeep

Jonathan Lewis wrote:
> "Pradeep" <agarwalp_at_eeism.com> wrote in message
> news:1132845637.997279.213440_at_o13g2000cwo.googlegroups.com...
> > Thanks for the answer Jonathan
> >
> >>> The redo is the bit that describes the change
> >>>to the undo segment header block that marks
> >>>the transaction as complete
> >
> > Isn't this the SCN?
> >
>
>
> No, the SCN is just a number being counted
> up somewhere in memory.
>
> To start a transaction you acquire a row (aka slot)
> in the transaction table that exists in each undo segment
> header block. This is the thing that your TX lock is
> locking. You update this row to show that your
> transaction is running, and to show the start SCN
> and a couple of other bits of information.
>
> To end a transaction, you update the row with
> the commit SCN, and flag the row to show that
> it is free. It is this change that is 'just another block
> change' and therefore described by a bit of redo,
> which the manuals (incorrectly) call the 'commit record'.
>
>
> --
> Regards
>
> Jonathan Lewis
>
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Received on Thu Nov 24 2005 - 22:13:04 CST