private DAGClient submitInternal(DAG dag, TezSessionState sessionState) throws TezException, IOException {
    runtimeContext.init(sessionState);
    return sessionState.getSession().submitDAG(dag);
  }
Ensures that the Tez Session is open and the AM has all necessary jars configured.
ql/src/java/org/apache/hadoop/hive/ql/exec/tez/TezTask.java