public MetricGroup group(String groupName, String... tagKeyValues) {
        MetricGroupId groupId = groupId(groupName, tagKeyValues);
        MetricGroup group = groupsByName.get(groupId);
        if (group == null) {
            group = new MetricGroup(groupId);
            MetricGroup previous = groupsByName.putIfAbsent(groupId, group);
            if (previous != null)
                group = previous;
        }
        return group;
    }
Get or create a {@link MetricGroup} with the specified group name and the given tags.
Each group is uniquely identified by the name and tags.

@param groupName    the name of the metric group; may not be null
@param tagKeyValues pairs of tag name and values
@return the {@link MetricGroup} that can be used to create metrics; never null
@throws IllegalArgumentException if the group name is not valid
connect/runtime/src/main/java/org/apache/kafka/connect/runtime/ConnectMetrics.java