@Override
    protected StorageID id0() {
        return new StorageID()
                .append(TIME_BUCKET, getTimeBucket())
                .append(ENTITY_ID, getEntityId());
    }
Service ID is required for sort query.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/analysis/meter/function/max/MaxLabeledFunction.java