Optimized xtern performance.
Optimized xtern performance.

columbia/xtern,hemingcui/xtern_with_paxos,columbia/xtern,hemingcui/xtern_with_paxos,hemingcui/xtern_with_paxos,hemingcui/xtern_with_paxos,columbia/xtern,columbia/xtern,hemingcui/xtern_with_paxos,columbia/xtern,columbia/xtern