Instead of building the map server as a player server plugin, I am now using memcached as my distributed map server.
Memcached allowed much faster access of map tiles. I also implemented tile lock so that multiple player plugins can update the same portion of the map at the same time.
Probability mapping, red means traversable space and blue is obstacle.
After growing the obstacles, the probability map is converted into configuration space map. This map can be easily used in global path planning. I also created a buffer zone near obstacles so the path planner will try to avoid those high cost area.