presto-main/src/main/java/io/prestosql/execution/TaskStateMachine.java/TaskStateMachine/toString
class TaskStateMachine:    @Override
    public String toString()
    {
        return toStringHelper(this)
                .add("taskId", taskId)
                .add("taskState", taskState)
                .add("failureCauses", failureCauses)
                .toString();
    }