The default timeout for the client's PeerCache is much longer than the DataNode would possibly keep the socket open. Specifically, dfs.client.socketcache.expiryMsec defaults to 2 *
60 * 1000 (2 minutes), whereas dfs.datanode.socket.reuse.keepalive
defaults to 1000 (1 second). We should make these more similar to minimize situations where the client tries to use sockets which have gone stale.