There are a few things about our
HDFS-4949 recaching strategy that could be improved.
- We should monitor the DN's maximum and current mlock'ed memory consumption levels, so that we don't ask the DN to do stuff it can't.
- We should not try to initiate caching on stale or decomissioning DataNodes (although we should not recache things stored on such nodes until they're declared dead).
- We might want to resend the DNA_CACHE or DNA_UNCACHE command a few times before giving up. Currently, we only send it once.