区分连接是mongod 还是mongos 的方式 或者副本集

db.isMaster()

Detect Connections to
mongos Instances

To detect if the MongoDB instance that your client is connectedto is
mongos, use the

isMaster command. When aclient connects to a

mongos,
isMaster returnsa document with a
msg field that holds the stringisdbgrid. For example:{
"ismaster" : true,
"msg" : "isdbgrid",
"maxBsonObjectSize" : 16777216,
"ok" : 1
}

If the application is instead connected to a
mongod, thereturned document does not include the
isdbgrid string.