一般的WEB應用如果是連ORACLE，要做連接池的話是在JAVA端用第三方的LIB，但對于MONGODB，官方已經有現成的實現，只需配置即可。
#控制系統在發生連接錯誤時是否重試 ，默認為false --boolean
mongo.options.autoConnectRetry=false
#每個主機允許的連接數（每個主機的連接池大小），當連接池被用光時，會被阻塞住 ，默認為10 --int
mongo.options.connectionsPerHost=10
#multiplier for connectionsPerHost for # of threads that can block if connectionsPerHost is 10, and threadsAllowedToBlockForConnectionMultiplier is 5, then 50 threads can block more than that and an exception will be throw --int
mongo.options.threadsAllowedToBlockForConnectionMultiplier=5
#被阻塞線程從連接池獲取連接的最長等待時間（ms） --int
mongo.options.maxWaitTime
#在建立（打開）套接字連接時的超時時間（ms），默認為0（無限） --int
mongo.options.connectTimeout=0
#套接字超時時間;該值會被傳遞給Socket.setSoTimeout(int)。默認為0（無限） --int
mongo.options.socketTimeout=0
#This controls whether or not to have socket keep alive turned on (SO_KEEPALIVE). defaults to false --boolean
mongo.options.socketKeepAlive=false
#Override the DBCallback factory. Default is for the standard Mongo Java driver configuration --DBCallbackFactory
mongo.options.dbCallbackFactory
#//指明是否允許驅動從次要節點或者奴隸節點讀取數據，默認為false --boolean
mongo.options.slaveOk=false
#如果為true，驅動每次update后會發出一個getLastError命令來保證成功，默認為false --boolean
mongo.options.safe=false
#If set, the w value of WriteConcern for the connection is set to this. Defaults to 0; implies safe = true --int
mongo.options.w=0
#If set, the wtimeout value of WriteConcern for the connection is set to this. Defaults to 0; implies safe = true --int
mongo.options.wtimeout=0
#Sets the fsync value of WriteConcern for the connection. Defaults to false; implies safe = true --boolean
mongo.options.fsync=false