Our zookeeper instances have very long uptimes on our cluster, and failed job trees are never cleaned from memory. There is a separate shell script to do this, but its not picky about which node trees it erases, and on some systems some Giraph users may not have access to it.
This patch will add a shell script to activate a new class which will use Giraph conf file options or our normal -Dgiraph.XYZ command-line opts to get the ZK quorum info, and clean out the remnants from its memory of old failed and killed jobs. They do pile up over time.
This led to the larger idea that Giraph needs a general giraph-admin shell script as a home for stuff like this. Jakob suggested it would be a good idea to put this into such a script since then admin groups can be created so that not every Giraph client can run it. This script currently only has code to start up the zk cleaner, but can have more options added to it as JIRA's to add features crop up.