MasterComputable defines master computation for any guagua application. All guagua application should define
its own master logic and to configure it by using guagua client configuration.
Any context parameters like current iteration, worker results can be got from
MasterContext.
To get global properties like Hadoop and YARN configuration properties,
MasterContext#getProps() is a wrapper
for Hadoop Configuration. Anything configured by using '-D' in command line can be got from these properties.
MasterContext#getWorkerResults() is the worker results from all the workers in current iteration. It can be
used for master computation logic.
Iteration starts from 1, ends with
MasterContext#getTotalIteration(). Total iteration number can be set in
command line through '-c' parameter.
MasterContext#getAppId() denotes the job ID for a map-reduce job in Hadoop, or YARN application ID for a YARN
application.
MasterContext#getContainerId() denotes current master container. It is task partition index in
Hadoop map-reduce job or split index in YARN guagua application. Container ID is unique for each master task, if
current master task is restarted after failure, it should use the same container id to make sure guagua know who it
is.