code: @Override
    public SpanConsumer spanConsumer() {
      if (spanConsumer == null) {
        synchronized (this) {
          if (spanConsumer == null) {
            spanConsumer = new CassandraSpanConsumer(this, indexCacheSpec);
          }
        }
      }
      return spanConsumer;
    }
docs: {@inheritDoc} Memoized in order to avoid re-preparing statements