code: public Future<Object> submitValidation(final ColumnFamilyStore cfStore, final Validator validator)
      {
          Callable<Object> callable = new Callable<Object>()
          {
              public Object call() throws IOException
              {
                  try
                  {
                      doValidationCompaction(cfStore, validator);
                  }
                  catch (Throwable e)
                  {
                      // we need to inform the remote end of our failure, otherwise it will hang on repair forever
                      validator.fail();
                      throw e;
                  }
                  return this;
              }
          };
          return validationExecutor.submit(callable);
      }
docs: Does not mutate data, so is not scheduled.