On Thu, 2008-08-07 at 10:56 -0400, Alvaro Herrera wrote:
> Simon Riggs wrote:
> > ii) have postmaster allow connections while Redo is taking place, as
> one
> > part of allowing query access to standby database
>
> is interesting and I'm sure it would be very welcome. Of course, it
> is first necessary to be able to run transactions in true "read only"
> mode, which perhaps is nowadays not so difficult given the work with
> VXids.
Maybe I am assuming that part is easier than I thought. Florian's
contribution with the VXid work should not be understated.
I was going to spread the setting of the global variable InRedo to all
backends, so they would be able to answer the question IsInRedo().
Anybody attempting to assign a new TransactionId would check this and
then exit with an ERROR. There would also be a check in XLogInsert(), in
case the first case doesn't catch everything or everyone. Transactions
would also run as read-only transactions to keep the front door locked.
Anything else you think needs bolting down?
-- Simon Riggs www.2ndQuadrant.comPostgreSQL Training, Services and Support