The perf test starts producing errors when it is run with --threads 11 (or higher). The cause is that we create a zookeeper connection per thread, and zookeeper recently added a feature which limits the number of connections per ip in
ZOOKEEPER-336. This setting is set to 10 by default. I recommend we bump this up in our packaged zk config, since it is hard to figure this out and makes it look like the client itself is having issues.