I found that the previous patch handles the ForeignScan's fs_relids Bitmapset destructively. Also, I noticed that I removed some existing comments inadvertently. So, I'm attaching the updated patch to fix those things. I'll add this to the next CF. I think this should be addressed in advance of the release of 9.6, though.
The patch is calculating user mapping when it's readily available through RelOptInfo::fdw_private. That incurs a catalog lookup unnecessarily. Instead, can we add new function makeOid, oidVal on the lines of makeInteger and intVal to store and retrieve an OID resp. and also corresponding print function? It might be helpful in future.
--
Best Wishes, Ashutosh Bapat EnterpriseDB Corporation The Postgres Database Company