Socket timeout exception in Mongo

Question

I see a few MongoExceptions caused by SocketTimeoutException (see the stack trace below). That is, client failed to get a response within the timeout (30 sec.). Now I wonder how to fix it.

The trivial solution is to increase the timeout but I'd like to understand the root cause first. What would you suggest?

caused by java.net.SocketTimeoutException: Read timed out
                 java.net.SocketInputStream.socketRead0 (Native Method)
                        java.net.SocketInputStream.read (SocketInputStream.java:152)
                        java.net.SocketInputStream.read (SocketInputStream.java:122)
                      java.io.BufferedInputStream.read1 (BufferedInputStream.java:273)
                       java.io.BufferedInputStream.read (BufferedInputStream.java:334)
                com.mongodb.Response$MyInputStream.read (Response.java:168)
               org.bson.BasicBSONDecoder$BSONInput.fill (BasicBSONDecoder.java:386)
     org.bson.BasicBSONDecoder$BSONInput.readUTF8String (BasicBSONDecoder.java:460)
                org.bson.BasicBSONDecoder.decodeElement (BasicBSONDecoder.java:155)
                      org.bson.BasicBSONDecoder._decode (BasicBSONDecoder.java:79)
                       org.bson.BasicBSONDecoder.decode (BasicBSONDecoder.java:57)
                    com.mongodb.DefaultDBDecoder.decode (DefaultDBDecoder.java:61)
                      com.mongodb.Response. (Response.java:83)
                                  com.mongodb.DBPort.go (DBPort.java:142)
                                com.mongodb.DBPort.call (DBPort.java:92)
                   com.mongodb.DBTCPConnector.innerCall (DBTCPConnector.java:244)
                        com.mongodb.DBTCPConnector.call (DBTCPConnector.java:216)
             com.mongodb.DBApiLayer$MyCollection.__find (DBApiLayer.java:288)
             com.mongodb.DBApiLayer$MyCollection.__find (DBApiLayer.java:273)
                       com.mongodb.DBCollection.findOne (DBCollection.java:728)
                       com.mongodb.DBCollection.findOne (DBCollection.java:708)

Answer 1

Did these time-outs happen after periods of inactivity? It's likely that your connection pool became stale after remaining idle for too long.

If so, there are two ways of going about this:

1. Catch the socket time-out exceptions, and your immediate request should be able to access a fresh connection pool. (this is if the auto-reconnect option in your connection object is left to true, which is default.)

2. Use a custom keep-alive, to ping the mongod server periodically using the same connection pool, so the pool remains fresh.

Option 1 is easy to implement, but the default socket time-out is around 30s which is rather excessive. You can change this setting as required.

Option 2 is a bit of a hack, involving threading.