Original discussion in newsgroup
Logstash transmits only windows_size - 1 events from a lumberjack output to a lumberjack input. After that it hangs waiting for an ack message.
lumberjack/client.rb:103
This appears to be fixed in the latest code in https://github.com/elasticsearch/logstash-forwarder, but that code is not present in 1.2.2's flatjar.
I was able to patch the flatjar by modifying the lumberjack client.rb file within the jar:
lumberjack/client.rb