Depends which Postgres version you are using: 9.1 added read only FDW support, 9.3 made it writable, 9.5 also has join pushdown into remote table.
Obviously, a lot depends on the FDW extension you are using - it doesn't help if there is support in postgres, if your specific extension does not utilize it.
Obviously, a lot depends on the FDW extension you are using - it doesn't help if there is support in postgres, if your specific extension does not utilize it.