Notes in-line.
--
Jonathan Lewis
http://www.jlcomp.demon.co.uk
Host to The Co-Operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html
Author of:
Practical Oracle 8i: Building Efficient Databases
Niall Litchfield wrote in message
<3cb1f96a$0$8505$cc9e4d1f_at_news.dial.pipex.com>...
>"Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message
>news:1018275095.8506.0.nnrp-12.9e984b29_at_news.demon.co.uk...
>>
>> It's telling you that Oracle can generate one undo record
>> per block modified, and doesn't always generate one undo
>> record per row modified.
>
>just musing/nitpicking but should that read one undo record per block
>modified per statement?
>
True - I had allowed that to be inferred from the context of
the discussion; but such inferences can easily lead to
misunderstandings.
>This opens up a whole interesting can of worms for me because I *know* (cos
>the docs and folk like Howard have told me so) that *in backup mode* that
>redo is generated for the whole block rather than the modified record(s)
>(assuming archivelog mode). Yet this is leading to a suggestion that redo
>*can* be in someways a snapshot of block level changes. which raises the
>question of how ordinary redo differs from *backup* redo.
>
I doubt if Howard told you that, as it's not quite true. In backup mode,
there is a very specific condition under which the entire current block
is copied into the redo buffer before the normal redo record is generated.
And contrary to common belief, this extreme action is not taken for
every redo change generated for the block.
Received on Mon Apr 08 2002 - 15:20:28 CDT
