public List<MetricsValues> readLabeledMetricsValuesWithoutEntity(String metricsName,
                                         List<KeyValue> labels,
                                         Duration duration) throws IOException {
        return getMetricQueryDAO().readLabeledMetricsValuesWithoutEntity(metricsName, ValueColumnMetadata.INSTANCE.getValueCName(metricsName), labels, duration);
    }
Read value in the given time duration, usually as a linear.

@param labels the labels you need to query.
oap-server/server-core/src/main/java/org/apache/skywalking/oap/server/core/query/MetricsQueryService.java