public SampleFamily downsampling(final DownsamplingType type) {
        ExpressionParsingContext.get().ifPresent(it -> it.downsampling = type);
        return this;
    }
Following operations are used in DSL
oap-server/analyzer/meter-analyzer/src/main/java/org/apache/skywalking/oap/meter/analyzer/dsl/SampleFamily.java