@Override
    public boolean combine(final Metrics metrics) {
        return true;
    }
Primary key(id), to identify a service with different layers, a service could have more than one layer and be
saved as different records.

@return Base64 encode(serviceName) + "." + layer.value
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/analysis/manual/service/ServiceTraffic.java