When sampling mechanism is off, why the method trySampling always return true ?

[thisisgpy]

When sampling mechanism is off, why the method org.apache.skywalking.apm.agent.core.sampling.SamplingService#trySampling always return true ?

/**
 * @param operationName The first operation name of the new tracing context.
 * @return true, if sampling mechanism is on, and getDefault the sampling factor successfully.
 */
public boolean trySampling(String operationName) {
    if (on) {
        int factor = samplingFactorHolder.get();
        if (factor < samplingRateWatcher.getSamplingRate()) {
            return samplingFactorHolder.compareAndSet(factor, factor + 1);
        } else {
            return false;
        }
    }
    return true;
}

[wu-sheng]

What do you mean? What do you expect?

[thisisgpy]

What do you mean? What do you expect?

From the method's comments, this method will return true only when the sampling mechanism is enabled and the samplingFactorHolder is successfully increased. But in the code, it will return true when the sampling mechanism is disabled. So what does the return value of this method mean? I think that only when true is returned, it means that a link can be sampled. But why is sampling allowed even when the sampling mechanism is enable?

[wu-sheng]

This comment needs some adjustments. It was 4 years ago, that comment is correct when sampling mechanism is ON.
The short version is return true means should sample.

Then correct comment is, welcome you to submit a pull request to correct this comment.

    /**
     * @param operationName The first operation name of the new tracing context.
     * @return true if should sample this trace segment. When sampling mechanism is on, return true if sample limited is not reached.
     */

[thisisgpy]

This comment needs some adjustments. It was 4 years ago, that comment is correct when sampling mechanism is ON. The short version is return true means should sample.

Then correct comment is, welcome you to submit a pull request to correct this comment.

    /**
     * @param operationName The first operation name of the new tracing context.
     * @return true if should sample this trace segment. When sampling mechanism is on, return true if sample limited is not reached.
     */

What I wonder is why it returns true when the sampling mechanism is disabled (when on = false).

[wu-sheng]

Sampling is OFF mean sampling 100% agent. If you don't want to sample any trace, uninstall the agent.

[wu-sheng]

Follow up #8227