Re: UNDO and in-place update

On 23/11/16 16:31, Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> [ Let's invent Oracle-style UNDO logs ]
>
> I dunno.  I remember being told years ago, by an ex-Oracle engineer,
> that he thought our approach was better.  I don't recall all the details
> of the conversation but I think his key point was basically this:
>
>> - Reading a page that has been recently modified gets significantly
>> more expensive; it is necessary to read the associated UNDO entries
>> and do a bunch of calculation that is significantly more complex than
>> what is required today.
>

Also ROLLBACK becomes vastly more expensive than COMMIT (I can recall 
many years ago when I used to be an Oracle DBA reading whole chapters of 
novels waiting for failed batch jobs to roll back).

However I'd like to add that I agree this is worth looking at, as 
ideally it would be great to be able to choose whether to have No-UNDO 
or UNDO on a table by table basis...

regards

Mark