@After
  public void teardown() {
    try {
      store.close();
    } catch (SamzaException e) {
      e.printStackTrace();
    }
  }
Make sure that the histograms can record the key value size and we can use a
{@link MetricsVisitor} to get access to the value store in the histograms
samza-test/src/test/java/org/apache/samza/storage/kv/TestKeyValueSizeHistogramMetric.java