void add(long indexTimestamp, Span span) {
      String index = consumer.formatTypeAndTimestampForInsert(TYPE_SPAN, indexTimestamp);
      bulkCallBuilder.index(index, TYPE_SPAN, span, spanWriter);
    }
Mutable type used for each call to store spans
zipkin-storage/elasticsearch/src/main/java/zipkin2/elasticsearch/ElasticsearchSpanConsumer.java