mognos:
ConnectionShardStatus preserve map<DBClientBase*, map<string,unsigned long long> > _map; to keep sequence number. when checkShardVersion , call setSequence to set de map, use key :
conn = getVersionable(&conn_in); (which is connection to master of replicaset when use shard and replicaset). but when shardconnection onDestroy, resetShardVersion use key　is ptr to shardconnection , not the connection to master of replicaset. So each time _map.erase(conn) return 0, and _map size always increase.

because i use short connection in web client , each time client close connection , mongos destroy shardconnection and cause _map increate. sometimes mongos create new connection to mongod, with same pointer position with an old connection object, cause the new connection can get an positive sequence from _map , of 0!. it will cause checkShardVersion run >2 times, and cause web client wait 3 -5 seconds.

i modify shard_version.cpp resetShardVersion function , when conn type is SET, connectionShardStatus.reset( getVersionable(conn) ); , fix this problem.