@Override public SpanConsumer spanConsumer() {
    if (spanConsumer == null) {
      synchronized (this) {
        if (spanConsumer == null) {
          spanConsumer = new CassandraSpanConsumer(this);
        }
      }
    }
    return spanConsumer;
  }
{@inheritDoc} Memoized in order to avoid re-preparing statements
zipkin-storage/cassandra/src/main/java/zipkin2/storage/cassandra/CassandraStorage.java