Re: Hot standby and b-tree killed items

On Friday 19 December 2008 05:52:42 Simon Riggs wrote:
> BTW, I noticed the other day that Oracle 11g only allows you to have a
> read only slave *or* allows you to continue replaying. You need to
> manually switch back and forth between those modes. They can't do
> *both*, as Postgres will be able to do. That's because their undo
> information is stored off-block in the Undo Tablespace, so is not
> available for standby queries. Nice one, Postgres.
>

I think this is true for physical replay, but Oracle also offers the option to 
do logical replay (where transaction logs are converted into sql and run 
against the standby; i believe this is similar to what continuant is trying 
to do with thier latest offering). In that scenario you can do read and 
replay at the same time, though I think there are some conflicts possible; 
fewer than what postgres will have, since I think most of thier DDL can be 
done online. (This might require some extra modules / high end version of 
Oracle, please consult your local Oracle wizard for more details)

-- 
Robert Treat
Conjecture: http://www.xzilla.net
Consulting: http://www.omniti.com