Re: Data Buffer Cache

Richard or anybody that cares to reply,
Only one small question. Which process is it that goes "to disk if not currently cached"?
Is this SMON? And is it the same process for instance recovery? thx
Mike

"Richard Foote" <richard.foote_at_bigpond.com> wrote in message news:rqwf9.29176$g9.84229_at_newsfeeds.bigpond.com...
> Hi All
>
> I know !!
>
> Firstly from a recovery point of view, indeed it is not possible for DBWR
 to
> write down something to disk that is not recorded in the redo logs. If the
> DBWR is "woken" up, it wakes up the LGWR to flush it's current contents
 down
> to disk.
>
> From a rollback point of view, it matters not if the undo block is in
 memory
> or disk. A rollback message requires Oracle to first access the changed
 data
> block (and go to disk if not currently cached). It then accesses the
> rollback segment header of the rollback segment that contains the undo in
> question (details of which are stored in the data block header) and go to
> disk if not currently in memory. Then it needs to retrieve the particular
> undo block referenced in the header to reconstruct the data block and
 apply
> the rollback (and go to disk if not currently cached).
 

> >
>
>
Received on Sat Sep 14 2002 - 15:12:52 CDT