How can I solve MongoWaitQueueFullException?

Question

I run a java program which is a thread executor program that inserts thousands of documents to a table in mongodb. I get the following error

Exception in thread "pool-1-thread-301" com.mongodb.MongoWaitQueueFullException: Too many threads are already waiting for a connection. Max number of threads (maxWaitQueueSize) of 500 has been exceeded.
    at com.mongodb.PooledConnectionProvider.get(PooledConnectionProvider.java:70)
    at com.mongodb.DefaultServer.getConnection(DefaultServer.java:73)
    at com.mongodb.BaseCluster$WrappedServer.getConnection(BaseCluster.java:221)
    at com.mongodb.DBTCPConnector$MyPort.getConnection(DBTCPConnector.java:508)
    at com.mongodb.DBTCPConnector$MyPort.get(DBTCPConnector.java:456)
    at com.mongodb.DBTCPConnector.getPrimaryPort(DBTCPConnector.java:414)
    at com.mongodb.DBCollectionImpl.insert(DBCollectionImpl.java:176)
    at com.mongodb.DBCollectionImpl.insert(DBCollectionImpl.java:159)
    at com.mongodb.DBCollection.insert(DBCollection.java:93)
    at com.mongodb.DBCollection.insert(DBCollection.java:78)
    at com.mongodb.DBCollection.insert(DBCollection.java:120)
    at ScrapResults103$MyRunnable.run(MyProgram.java:368)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
    at java.lang.Thread.run(Thread.java:695)

How can I resolve this? Please help me.

Answer 1

You need to check what is the connections per host value which you have given while setting up connection (looking at the exception I think you would have set it to 500).

MongoClientOptions.Builder builder = new MongoClientOptions.Builder();
builder.connectionsPerHost(200);
MongoClientOptions options = builder.build();
mongoClient = new MongoClient(URI, connectionOptions);

An ideal way of setting the connections per host would be by trial and error but you need to make sure that the value which you set should not exceed the number of connections you can have by opening the mongo shell and executing:

db.serverStatus().connections.available

Answer 2

you are in maxWaitQueueSize limit , so increase multiplier ;)

 MongoClientOptions options = MongoClientOptions.builder()
                .threadsAllowedToBlockForConnectionMultiplier(10)
                .build();

 MongoClient mongo = new MongoClient("127.0.0.1:27017", options);
 //run 2000 threads and use database ;)