> I would think that the data pages are written and consistent while in > recovery mode, so maybe it's reasonable to do. However, I'm only > speculating and anything like this would probably not be coming soon. I was thinking at one point about what problems could prevent the standby to allow read only access, and got to the conclusion that it would be difficult to assure consistency. Think about it: you start a read only transaction on the standby, but if the standby continues to apply changes from the master, it is entirely possible it will rewrite/delete some pages which contain data which your read only transaction should be able to see, but it won't see it. So to make the read only transactions consistent, the standby would be required to stop applying changes which are newer than the oldest read only transaction running. That would mean you will have a backlog of WAL records to apply at least as big as the age of your oldest running read only transaction, therefore the data will be delayed the same compared to the master, which might be OK for some scenarios... Of course there might be other problems too. Cheers, Csaba.
