private void setAttrCacheTag(MetricsTag tag, int recNo) {
   String key = tagName(tag.name(), recNo);
   attrCache.put(key, new Attribute(key, tag.value()));
 }
 @Override
 public MetricsRecordBuilder add(MetricsTag metricsTag) {
   tags.put(canonicalizeMetricName(metricsTag.name()), metricsTag.value());
   return this;
 }