When Solr gets into pathological GC thrashing states, it can fill the overseer queue with literally thousands and thousands of queued state changes. Many of these end up being duplicated up/down state updates. Our production cluster has gotten to the 100k queued items level many times, and there's nothing useful you can do at this point except manually purge the queue in ZK. Recently, it hit 3 million queued items, at which point our entire ZK cluster exploded.
I propose a hard cap. Any client trying to enqueue a item when a queue is full would throw an exception. I was thinking maybe 10,000 items would be a reasonable limit. Thoughts?