BUG#13987 Cluster: Loss of data nodes can cause high CPU usage from ndb_mgmd
BUG#13987 Cluster: Loss of data nodes can cause high CPU usage from ndb_mgmd

A further reduction in CPU usage by ndb_mgmd with failed data nodes.


ndb/src/common/util/socket_io.cpp:
  Use a nonblocking socket to peek at the buffer to know how much to read for socket_readln.
  
  This saves us a lot of syscalls. By a lot, I've observed about halving the CPU
  usage of ndb_mgmd with 1 failed node on a 6 node cluster.

ollie314/server,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,davidl-zend/zenddbi,flynn1973/mariadb-aix,ollie314/server,natsys/mariadb_10.2,flynn1973/mariadb-aix,davidl-zend/zenddbi,flynn1973/mariadb-aix,davidl-zend/zenddbi,flynn1973/mariadb-aix,davidl-zend/zenddbi,ollie314/server,flynn1973/mariadb-aix,davidl-zend/zenddbi,ollie314/server,ollie314/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,natsys/mariadb_10.2,ollie314/server,ollie314/server,ollie314/server,ollie314/server,davidl-zend/zenddbi,natsys/mariadb_10.2,davidl-zend/zenddbi,flynn1973/mariadb-aix,flynn1973/mariadb-aix,flynn1973/mariadb-aix,ollie314/server,davidl-zend/zenddbi,davidl-zend/zenddbi,flynn1973/mariadb-aix,davidl-zend/zenddbi,slanterns/server,natsys/mariadb_10.2,ollie314/server,davidl-zend/zenddbi,natsys/mariadb_10.2,natsys/mariadb_10.2,flynn1973/mariadb-aix