ElasticSearch server and java client both have an unbound, undocumented threadpool that can cause lockup of the whole JVM process and take down the whole server machine: #5151.

The minimum change is documenting the unbound generic pool & instructions for reconfiguring it at http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/modules-threadpool.html.

IMHO unbound threadpool is a Bad Idea from the start. Bound pool with some reasonable size queue and abort policy would not cause jvm/server lockup in a runaway case, instead you would get some meaningful information in the log.