static long traceIdHigh(PeekingIterator<Record> delegate) {
    return delegate.peek().getValue(ZipkinSpans.ZIPKIN_SPANS.TRACE_ID_HIGH);
  }
Assumes the input records are sorted by trace id, span id
zipkin-storage/mysql-v1/src/main/java/zipkin2/storage/mysql/v1/DependencyLinkV2SpanIterator.java