code: public boolean isSampled(String hexTraceId, boolean debug) {
      if (Boolean.TRUE.equals(debug)) return true;
      long traceId = HexCodec.lowerHexToUnsignedLong(hexTraceId);
      // The absolute value of Long.MIN_VALUE is larger than a long, so Math.abs returns identity.
      // This converts to MAX_VALUE to avoid always dropping when traceId == Long.MIN_VALUE
      long t = traceId == Long.MIN_VALUE ? Long.MAX_VALUE : Math.abs(traceId);
      return t <= boundary();
    }
docs: Returns true if spans with this trace ID should be recorded to storage.
  
  <p>Zipkin v1 allows storage-layer sampling, which can help prevent spikes in traffic from
  overloading the system. Debug spans are always stored.
  
  <p>This uses only the lower 64 bits of the trace ID as instrumentation still send mixed trace
  ID width.
  
  @param hexTraceId the lower 64 bits of the span's trace ID are checked against the boundary
  @param debug when true, always passes sampling