public SamplingPolicy get(String service) {
        return this.services.get(service);
    }
The sample rate precision is 1/10000. 10000 means 100% sample in default. Setting this threshold about the
latency would make the slow trace segments sampled if they cost more time, even the sampling mechanism activated.
The default value is `-1`, which means would not sample slow traces. Unit, millisecond.
oap-server/analyzer/agent-analyzer/src/main/java/org/apache/skywalking/oap/server/analyzer/provider/trace/sampling/SamplingPolicySettings.java