public static ValueJoiner<Article, Long, AugmentedArticle> joiner() {
            return (article, commentCount) -> new AugmentedArticle(
                article.getKey(),
                article.getTimestamp(),
                article.getText(), commentCount == null ? 0 : commentCount
            );
        }
Generates a keySpace number of unique keys normally distributed,
with the mean at 0 and stdDev 1/3 of the way through the keySpace
any sample more than 3 standard deviations from the mean are assigned to the 0 key.
<p>
This is designed to roughly balance the key properties of two dominant real-world
data distribution: Zipfian and Normal, while also being efficient to generate.
streams/src/test/java/org/apache/kafka/streams/tests/RelationalSmokeTest.java