I see a lot of "transport errors" like the ones below in my application, and I can't figure out why. I've had to guard every call to mongo in my application with a lot of error handling logic just to avoid keeling over every time it throws a OperationFailure.

Here's a grep for "transport error" from a mongos.log, all these happened yesterday (there's tons more in the logs for previous days):

Mon Jul 18 08:55:40 [WriteBackListener] WriteBackListener exception : DBClientBase::findOne: transport error: rfmcolldb05:27017 query:

{ writebacklisten: ObjectId('4e16ba0635330bc016259dc4') }

Mon Jul 18 16:25:27 [conn659] warning: Could not get last error.DBClientBase::findOne: transport error: rfmcolldb06:27117 query:

{ getlasterror: 1 }

Mon Jul 18 16:25:27 [WriteBackListener] WriteBackListener exception : DBClientBase::findOne: transport error: rfmcolldb06:27117 query:

{ writebacklisten: ObjectId('4e16ba0635330bc016259dc4') }

Mon Jul 18 16:25:27 [Balancer] caught exception while doing balance: DBClientBase::findOne: transport error: rfmcolldb06:27117 query:

{ features: 1 }

Mon Jul 18 16:25:27 [conn664] warning: Could not get last error.DBClientBase::findOne: transport error: rfmcolldb06:27117 query:

{ getlasterror: 1 }

Mon Jul 18 16:35:14 [WriteBackListener] WriteBackListener exception : DBClientBase::findOne: transport error: rfmcolldb01:27017 query:

{ writebacklisten: ObjectId('4e16ba0635330bc016259dc4') }

Mon Jul 18 16:43:53 [WriteBackListener] WriteBackListener exception : DBClientBase::findOne: transport error: rfmcolldb01:27117 query:

{ writebacklisten: ObjectId('4e16ba0635330bc016259dc4') }

Mon Jul 18 16:43:53 [conn685] warning: Could not get last error.DBClientBase::findOne: transport error: rfmcolldb01:27117 query:

{ getlasterror: 1 }

Mon Jul 18 16:43:53 [Balancer] caught exception while doing balance: DBClientBase::findOne: transport error: rfmcolldb01:27117 query:

{ features: 1 }

Mon Jul 18 17:08:48 [WriteBackListener] WriteBackListener exception : DBClientBase::findOne: transport error: rfmcolldb04:27117 query:

{ writebacklisten: ObjectId('4e16ba0635330bc016259dc4') }

Mon Jul 18 17:09:02 [WriteBackListener] WriteBackListener exception : DBClientBase::findOne: transport error: rfmcolldb04:27017 query:

{ writebacklisten: ObjectId('4e16ba0635330bc016259dc4') }

Mon Jul 18 17:09:02 [Balancer] caught exception while doing balance: DBClientBase::findOne: transport error: rfmcolldb04:27017 query:

{ features: 1 }

Mon Jul 18 17:09:08 [WriteBackListener] WriteBackListener exception : DBClientBase::findOne: transport error: rfmcolldb05:27117 query:

{ writebacklisten: ObjectId('4e16ba0635330bc016259dc4') }

Mon Jul 18 17:15:08 ERROR: couldn't unset sharding : DBClientBase::findOne: transport error: rfmcolldb05:27117 query:

{ unsetSharding: 1 }

Mon Jul 18 17:19:44 [WriteBackListener] ERROR: error processing writeback: 10276 DBClientBase::findOne: transport error: rfmcolldb04:27017 query: { setShardVersion: "fragments.pageview_fragments", configdb: "rfmcolldb01:28100,rfmcolldb0
Mon Jul 18 17:20:17 [WriteBackListener] ERROR: error processing writeback: 10276 DBClientBase::findOne: transport error: rfmcolldb05:27117 query: { setShardVersion: "complete.exposures", configdb: "rfmcolldb01:28100,rfmcolldb02:28100,rf
Mon Jul 18 17:20:56 [WriteBackListener] ERROR: error processing writeback: 10276 DBClientBase::findOne: transport error: rfmcolldb05:27117 query:

{ getlasterror: 1 }

Mon Jul 18 18:20:05 [WriteBackListener] ERROR: error processing writeback: 10276 DBClientBase::findOne: transport error: rfmcolldb04:27017 query:

{ getlasterror: 1 }

Mon Jul 18 22:10:17 [WriteBackListener] WriteBackListener exception : DBClientBase::findOne: transport error: rfmcolldb03:27117 query:

{ writebacklisten: ObjectId('4e16ba0635330bc016259dc4') }

Mon Jul 18 22:10:30 [WriteBackListener] WriteBackListener exception : DBClientBase::findOne: transport error: rfmcolldb03:27017 query:

{ writebacklisten: ObjectId('4e16ba0635330bc016259dc4') }

Mon Jul 18 22:10:30 [conn1374] warning: Could not get last error.DBClientBase::findOne: transport error: rfmcolldb03:27017 query:

{ getlasterror: 1 }

Mon Jul 18 22:10:31 [WriteBackListener] WriteBackListener exception : DBClientBase::findOne: transport error: rfmcolldb03:27017 query:

{ writebacklisten: ObjectId('4e16ba0635330bc016259dc4') }

Mon Jul 18 22:10:31 ERROR: couldn't unset sharding : DBClientBase::findOne: transport error: rfmcolldb03:27017 query:

{ unsetSharding: 1 }

Mon Jul 18 22:10:31 ERROR: couldn't unset sharding : DBClientBase::findOne: transport error: rfmcolldb03:27017 query:

{ unsetSharding: 1 }

Mon Jul 18 22:10:31 ERROR: couldn't unset sharding : DBClientBase::findOne: transport error: rfmcolldb03:27017 query:

{ unsetSharding: 1 }

Mon Jul 18 22:10:31 ERROR: couldn't unset sharding : DBClientBase::findOne: transport error: rfmcolldb03:27017 query:

{ unsetSharding: 1 }

Mon Jul 18 22:10:33 [WriteBackListener] WriteBackListener exception : DBClientBase::findOne: transport error: rfmcolldb03:27017 query:

{ writebacklisten: ObjectId('4e16ba0635330bc016259dc4') }

Mon Jul 18 22:10:43 [WriteBackListener] ERROR: error processing writeback: 10276 DBClientBase::findOne: transport error: rfmcolldb02:27017 query: { setShardVersion: "fragments.exposure_fragments", configdb: "rfmcolldb01:28100,rfmcolldb0
Mon Jul 18 22:10:43 [WriteBackListener] ERROR: error processing writeback: 10276 DBClientBase::findOne: transport error: rfmcolldb02:27017 query: { setShardVersion: "fragments.exposure_fragments", configdb: "rfmcolldb01:28100,rfmcolldb0