Flume 1.6 Thrift source issues

[Tobias Heintz <to...@plista.com>]

Hello!

We are in the process of migrating from the old Flume to version 1.6. We are using the ThriftSource with the new KafkaSink. Here's what our config looks like:

```
agent1.channels = ch1
agent1.sources = thriftSrc
agent1.sinks = kafka

agent1.channels.ch1.type = memory
agent1.channels.ch1.capacity = 10000
agent1.channels.ch1.transactionCapacity = 500

# THRIFT
agent1.sources.thriftSrc.type = thrift
agent1.sources.thriftSrc.channels = ch1
agent1.sources.thriftSrc.bind = 0.0.0.0
agent1.sources.thriftSrc.port = 4042
agent1.sources.thriftSrc.threads = 150 # if we don't set this option, the source keeps creating more and more threads until all heap memory is used up and then it crashes

# KAFKA
agent1.sinks.kafka.channel = ch1
agent1.sinks.kafka.type = org.apache.flume.sink.kafka.KafkaSink
agent1.sinks.kafka.batchSize = 50
agent1.sinks.kafka.brokerList = broker.example.com:9092
agent1.sinks.kafka.requiredAcks = 1
agent1.sinks.kafka.topic = topic1
```

We have been noticing some bad behavior by the Thrift source/Thrift server using the JMX connection. If we don't restrict the number of threads, it spawns thousands of new threads, apparently one for every message it receives. These threads all have the name "Flume Thrift IPC Thread [number]" and according to the jvisualvm console they are always idle. At some point all of the JVM memory is used up through creating new threads and flume crashes with the following exception:
```
12 Aug 2015 16:56:11,721 ERROR [Thread-1] (org.apache.thrift.server.TThreadedSelectorServer$SelectorThread.run:544)  - run() exiting due to uncaught error
java.lang.OutOfMemoryError: unable to create new native thread
        at java.lang.Thread.start0(Native Method)
        at java.lang.Thread.start(Thread.java:714)
        at java.util.concurrent.ThreadPoolExecutor.addWorker(ThreadPoolExecutor.java:949)
        at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1360)
        at org.apache.thrift.server.TThreadedSelectorServer.requestInvoke(TThreadedSelectorServer.java:310)
        at org.apache.thrift.server.AbstractNonblockingServer$AbstractSelectThread.handleRead(AbstractNonblockingServer.java:209)
        at org.apache.thrift.server.TThreadedSelectorServer$SelectorThread.select(TThreadedSelectorServer.java:576)
        at org.apache.thrift.server.TThreadedSelectorServer$SelectorThread.run(TThreadedSelectorServer.java:536)
```

When we set the option to restrict the number of threads, the server sticks to that number and runs smoothly, however it drops messages occasionally (may have a different cause).

I am wondering whether this is a bug or in some way expected behavior? What are the best practices for using a ThriftSource? Are there further parameters to possibly tune (like channel.capacity)?

Thanks a lot


--
Tobias Heintz