@UnstableApi
    public AbstractLoggingClientBuilder failureSampler(
            Sampler<? super ClientRequestContext> failureSampler) {
        this.failureSampler = requireNonNull(failureSampler, "failureSampler");
        return this;
    }
Sets the {@link Sampler} that determines which failure request needs logging.
core/src/main/java/com/linecorp/armeria/client/logging/AbstractLoggingClientBuilder.java