func (t *tierMetrics) logSuccess(tier string) {
	t.Lock()
	defer t.Unlock()

	stat := t.requestsCount[tier]
	stat.success++
	t.requestsCount[tier] = stat
}

func (t *tierMetrics) logFailure(tier string) {
	t.Lock()
	defer t.Unlock()

	stat := t.requestsCount[tier]
	stat.failure++
	t.requestsCount[tier] = stat
}

var (
	// {minio_node}_{tier}_{ttlb_seconds_distribution}

   * missRate =~ 1.0}.
   */
  public double hitRate() {
    long requestCount = requestCount();
    return (requestCount == 0) ? 1.0 : (double) hitCount / requestCount;
  }

  /**
   * Returns the number of times {@link Cache} lookup methods have returned an uncached (newly
   * loaded) value, or null. Multiple concurrent calls to {@link Cache} lookup methods on an absent

   * missRate =~ 1.0}.
   */
  public double hitRate() {
    long requestCount = requestCount();
    return (requestCount == 0) ? 1.0 : (double) hitCount / requestCount;
  }

  /**
   * Returns the number of times {@link Cache} lookup methods have returned an uncached (newly
   * loaded) value, or null. Multiple concurrent calls to {@link Cache} lookup methods on an absent

    assertEquals(EMPTY_STATS, cache.stats());

    Object one = new Object();
    cache.getUnchecked(one);
    CacheStats stats = cache.stats();
    assertEquals(1, stats.requestCount());
    assertEquals(0, stats.hitCount());
    assertThat(stats.hitRate()).isEqualTo(0.0);
    assertEquals(1, stats.missCount());
    assertThat(stats.missRate()).isEqualTo(1.0);
    assertEquals(1, stats.loadCount());

    assertEquals(EMPTY_STATS, cache.stats());

    Object one = new Object();
    cache.getUnchecked(one);
    CacheStats stats = cache.stats();
    assertEquals(1, stats.requestCount());
    assertEquals(0, stats.hitCount());
    assertThat(stats.hitRate()).isEqualTo(0.0);
    assertEquals(1, stats.missCount());
    assertThat(stats.missRate()).isEqualTo(1.0);
    assertEquals(1, stats.loadCount());

                                  Valid Options: ALL_METRICS, REQUEST_COUNT, REQUEST_DURATION, REQUEST_SIZE, RESPONSE_SIZE, TCP_OPENED_CONNECTIONS, TCP_CLOSED_CONNECTIONS, TCP_SENT_BYTES, TCP_RECEIVED_BYTES, GRPC_REQUEST_MESSAGES, GRPC_RESPONSE_MESSAGES
                                enum:
                                - ALL_METRICS
                                - REQUEST_COUNT
                                - REQUEST_DURATION