MongoDB连接池耗尽

异常日志：

Out of semaphores to get db connection 
查看源代码发现是连接池资源用尽： 

查代码看原因：

DBPortPool 写道

if ( ! _waitingSem.tryAcquire() )
throw new SemaphoresOut();

_waitingSem初始化代码

DBPortPool 写道

_waitingSem = new Semaphore( _options.connectionsPerHost * _options.threadsAllowedToBlockForConnectionMultiplier );

MongoOptions 写道

public MongoOptions(){
reset();
}

public void reset(){
connectionsPerHost = Bytes.CONNECTIONS_PER_HOST;
threadsAllowedToBlockForConnectionMultiplier = 5;
maxWaitTime = 1000 * 60 * 2;
connectTimeout = 0;
socketTimeout = 0;
socketKeepAlive = false;
autoConnectRetry = false;
maxAutoConnectRetryTime = 0;
slaveOk = false;
safe = false;
w = 0;
wtimeout = 0;
fsync = false;
j = false;
dbDecoderFactory = DefaultDBDecoder.FACTORY;
socketFactory = SocketFactory.getDefault();
}

其中：

static final int CONNECTIONS_PER_HOST = Integer.parseInt( System.getProperty( "MONGO.POOLSIZE" , "10" ) );

改变连接池大小：

1、可以通过系统属性改变连接池大小。

2、代码层面修改，new Mongo的时，先一个你需要的MongoOptions