It is my impression that there still are several people having pretty fundamental doubts about this approach in general. From what I remember neither Heikki, Simon, Tom nor me were really convinced about this approach.
IIRC you and Tom were particularly skeptical about the approach. But do you see a technical flaw or a show stopper with the approach ? Heikki has written pg_rewind which is really very cool. But it fails to handle the hint bit updates which are not WAL logged unless of course checksums are turned on. We can have a GUC controlled option to turn WAL logging on for hint bit updates and then use pg_rewind for the purpose. But I did not see any agreement on that either. Performance implication of WAL logging every hint bit update could be huge.
Simon has raised usability concerns that Sawada-san and Samrat have tried to address by following his suggestions. I am not fully convinced though we have got that right. But then there is hardly any feedback on that aspect lately.
In general, from the discussion it seems that the patch is trying to solve a real problem. Even though Tom and you feel that rsync is probably good enough and more trustworthy than any other approach, my feeling is that many including Fujii-san still disagree with that argument based on real user feedback. So where do we go from here ? I think it will really help Sawada-san and Samrat if we can provide them some solid feedback and approach to take.
Lately, I was thinking if we could do something else to track file system updates without relying on WAL inspection and then use pg_rewind to solve this problem. Some sort of prelaod library mechanism is one such possibility. But haven't really thought through this entirely.
