At work, I've been working on bi-directional replication for Postgres. It even works already, though only some parts of it have been merged into 9.4-to-be so far (and more are targeted for next year, in 9.5).
I'll look at how to implement Arnt's renumbering scheme there. (I've never looked at Postgres-XC in any detail.) -- ams P.S. https://wiki.postgresql.org/wiki/BDR_User_Guide
