Re: Hot standby and b-tree killed items

On Fri, 2008-12-19 at 19:29 -0500, Robert Treat wrote:
> 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. 

That is also an option I have argued that we need, BTW.

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Training, Services and Support