Over on pig-dev, Sam Pullara pointed out the following Java mechanism
that permits one to be notified when memory usage exceeds a threshold.
http://java.sun.com/javase/6/docs/api/java/lang/management/MemoryPoolMXBean.html#UsageThreshold
Perhaps we could use something like this on the namenode? For example,
when memory usage is too high, the namenode could refuse creation of new
files. This would still crash applications, but it would keep the
filesystem itself from crashing in a way that is hard to recover while
folks remove excessive (presumably) small files.
Doug
