private void readDefaultSamplingPolicy(SamplingPolicySettings samplingPolicySettings) {
        Map<String, Object> objectMap = (Map<String, Object>) yamlData.get("default");
        if (objectMap == null) {
            return;
        }
        if (objectMap.get("rate") != null) {
            samplingPolicySettings.getDefaultPolicy().setRate((Integer) objectMap.get("rate"));
        }
        if (objectMap.get("duration") != null) {
            samplingPolicySettings.getDefaultPolicy().setDuration((Integer) objectMap.get("duration"));
        }
    }
Read policy config file to {@link SamplingPolicySettings}
oap-server/analyzer/agent-analyzer/src/main/java/org/apache/skywalking/oap/server/analyzer/provider/trace/sampling/SamplingPolicySettingsReader.java