private void execute() throws CommandProcessorException {
    try {
      taskQueue = new TaskQueue(context); // for canceling the query (should be bound to session?)
      Executor executor = new Executor(context, driverContext, driverState, taskQueue);
      executor.execute();
    } catch (CommandProcessorException cpe) {
      driverTxnHandler.rollback(cpe);
      saveErrorMessageAndRethrow(cpe);
    }
  }
Checks if the recorded snapshot is up-to-date
ql/src/java/org/apache/hadoop/hive/ql/Driver.java