On Fri, Jun 14, 2013 at 4:12 PM, Heikki Linnakangas <hlinnakan...@vmware.com > wrote:
> Robert Haas pointed out in that thread that it has a problem with hint > bits that are not WAL-logged, > I liked that tool a lot until Robert pointed out the above problem. I thought this is a show stopper because I can't really see any way to circumvent it unless we enable checksums or explicitly WAL log hint bits. > but it will still work if you also enable the new checksums feature, which > forces hint bit updates to be WAL-logged. > Are we expecting a lot of people to run their clusters with checksums on ? Sorry, I haven't followed the checksum discussions and don't know how much overhead it causes. But if the general expectation is that checksums will be turned on most often, I agree pg_rewind is probably good enough. > Perhaps we could add a GUC to enable hint bits to be WAL-logged, > regardless of checksums, to make pg_rewind work. > > Wouldn't that be too costly ? I mean, in the worst case every hint bit on a page may get updated separately. If each such update is WAL logged, we are looking for a lot more unnecessary WAL traffic. > I think that's a more flexible approach to solve this problem. It doesn't > require an online feedback loop from the standby to master, for starters. > > I agree. That's a big advantage of pg_rewind. Unfortunately, it can't work with 9.3 and below because of the hint bits issue, otherwise it would have been even more cool. Thanks, Pavan -- Pavan Deolasee http://www.linkedin.com/in/pavandeolasee
