Affects Version/s: None
Fix Version/s: 0.18.0
HADOOP-2910 changed HDFS to stop accepting new connections when the rpc queue is full. It should continue to accept connections and let the OS deal with limiting connections. HADOOP-2910's decision to not read from open sockets when queue is full is exactly right - backup on the
client sockets and they will just wait( especially with
HADOOP-2188 that removes client timeouts).
However we should continue to accept connections:
The OS refuses new connections after a large number of connections are open (this is configurable parameter). With this patch, we have new lower limit for # of open connections when the RPC queue is full.
The problem is that when there is a surge of requests, we would stop
accepting connection and clients will get a connection failed (a change from old behavior).
Instead if you continue to accept connections it is likely that the surge will be over shortly and
clients will get served. Of course if the surge lasts a long time the OS will stop accepting connections
and clients will fail and there not much one can do (except raise the os limit).
I propose that we continue accepting connections, but not read from
connections when the RPC queue is full. (ie undo part of 2910 work back to the old behavior).