CacheMetrics: Switch to APITimer

CacheMetrics is a general counter that is used for all possible caches.
For caches that we do not support, there is no need to go and fetch
their values.

When moving to the APITimer each such request will take longer (the
value will not be available as it use it) now it will be possible to
supply a null as a url which would cause to the metrics to return 0 for
all counters.

Signed-off-by: Amnon Heiman <amnon@scylladb.com>

src/main/java/org/apache/cassandra/metrics/CacheMetrics.java

@@ -31,7 +31,7 @@ import com.scylladb.jmx.metrics.APIMetrics;
 import com.scylladb.jmx.metrics.DefaultNameFactory;
 import com.scylladb.jmx.metrics.MetricNameFactory;
 import com.yammer.metrics.core.Gauge;
-import com.yammer.metrics.core.Meter;
+import com.yammer.metrics.core.APIMeter;
 
 /**
  * Metrics for {@code ICache}.
@@ -40,9 +40,9 @@ public class CacheMetrics {
     /** Cache capacity in bytes */
     public final Gauge<Long> capacity;
     /** Total number of cache hits */
-    public final Meter hits;
+    public final APIMeter hits;
     /** Total number of cache requests */
-    public final Meter requests;
+    public final APIMeter requests;
     /** cache hit rate */
     public final Gauge<Double> hitRate;
     /** Total size of cache, in bytes */
@@ -55,6 +55,12 @@ public class CacheMetrics {
 
     private APIClient c = new APIClient();
 
+    private String getURL(String url, String value) {
+        if (url == null || value == null) {
+            return null;
+        }
+        return "/cache_service/metrics/" + url + value;
+    }
     /**
      * Create metrics for given cache.
      *
@@ -66,39 +72,50 @@ public class CacheMetrics {
     public CacheMetrics(String type, final String url) {
         MetricNameFactory factory = new DefaultNameFactory("Cache", type);
 
+
         capacity = APIMetrics.newGauge(factory.createMetricName("Capacity"),
                 new Gauge<Long>() {
+                    String u = getURL(url, "/capacity");
                     public Long value() {
-                        return c.getLongValue("/cache_service/metrics/" + url
-                                + "/capacity");
+                        if (u == null) {
+                            return 0L;
+                        }
+                        return c.getLongValue(u);
                     }
                 });
-        hits = APIMetrics.newMeter("/cache_service/metrics/" + url
-                + "/hits", factory.createMetricName("Hits"), "hits",
+        hits = APIMetrics.newMeter(getURL(url, "/hits_moving_avrage"), factory.createMetricName("Hits"), "hits",
                 TimeUnit.SECONDS);
-        requests = APIMetrics.newMeter("/cache_service/metrics/" + url
-                + "/requests", factory.createMetricName("Requests"),
+        requests = APIMetrics.newMeter(getURL(url, "/requests_moving_avrage"), factory.createMetricName("Requests"),
                 "requests", TimeUnit.SECONDS);
         hitRate = APIMetrics.newGauge(factory.createMetricName("HitRate"),
                 new Gauge<Double>() {
+                    String u = getURL(url, "/hit_rate");
                     @Override
                     public Double value() {
-                        return c.getDoubleValue("/cache_service/metrics/" + url
-                                + "/hit_rate");
+                        if (u == null) {
+                            return 0.0;
+                        }
+                        return c.getDoubleValue(u);
                     }
                 });
         size = APIMetrics.newGauge(factory.createMetricName("Size"),
                 new Gauge<Long>() {
+                    String u = getURL(url, "/size");
                     public Long value() {
-                        return c.getLongValue("/cache_service/metrics/" + url
-                                + "/size");
+                        if (u == null) {
+                            return 0L;
+                        }
+                        return c.getLongValue(u);
                     }
                 });
         entries = APIMetrics.newGauge(factory.createMetricName("Entries"),
                 new Gauge<Integer>() {
+                    String u = getURL(url, "/entries");
                     public Integer value() {
-                        return c.getIntValue("/cache_service/metrics/" + url
-                                + "/entries");
+                        if (u == null) {
+                            return 0;
+                        }
+                        return c.getIntValue(u);
                     }
                 });
     }