Adding the CacheMetrics class

The CacheMetrics holds information per a specific Cache type (key, row
or counter)

It the clas was modified to use the API. The API definition can be found
in cache_service.json under metrics.

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

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

@@ -0,0 +1,106 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * Copyright 2015 Cloudius Systems
+ *
+ * Modified by Cloudius Systems
+ */
+package org.apache.cassandra.metrics;
+
+import java.util.concurrent.TimeUnit;
+import com.cloudius.urchin.api.APIClient;
+import com.cloudius.urchin.metrics.APIMetrics;
+import com.cloudius.urchin.metrics.DefaultNameFactory;
+import com.cloudius.urchin.metrics.MetricNameFactory;
+import com.yammer.metrics.core.Gauge;
+import com.yammer.metrics.core.Meter;
+
+/**
+ * Metrics for {@code ICache}.
+ */
+public class CacheMetrics {
+    /** Cache capacity in bytes */
+    public final Gauge<Long> capacity;
+    /** Total number of cache hits */
+    public final Meter hits;
+    /** Total number of cache requests */
+    public final Meter requests;
+    /** cache hit rate */
+    public final Gauge<Double> hitRate;
+    /** Total size of cache, in bytes */
+    public final Gauge<Long> size;
+    /** Total number of cache entries */
+    public final Gauge<Integer> entries;
+
+    private APIClient c = new APIClient();
+
+    /**
+     * Create metrics for given cache.
+     *
+     * @param type
+     *            Type of Cache to identify metrics.
+     * @param cache
+     *            Cache to measure metrics
+     */
+    public CacheMetrics(String type, String url) {
+        MetricNameFactory factory = new DefaultNameFactory("Cache", type);
+
+        capacity = APIMetrics.newGauge(factory.createMetricName("Capacity"),
+                new Gauge<Long>() {
+                    public Long value() {
+                        return c.getLongValue("/cache_service/metrics/" + url
+                                + "/capacity");
+                    }
+                });
+        hits = APIMetrics.newMeter("/cache_service/metrics/" + url
+                + "/hits", factory.createMetricName("Hits"), "hits",
+                TimeUnit.SECONDS);
+        requests = APIMetrics.newMeter("/cache_service/metrics/" + url
+                + "/requests", factory.createMetricName("Requests"),
+                "requests", TimeUnit.SECONDS);
+        hitRate = APIMetrics.newGauge(factory.createMetricName("HitRate"),
+                new Gauge<Double>() {
+                    @Override
+                    public Double value() {
+                        return c.getDoubleValue("/cache_service/metrics/" + url
+                                + "/hit_rate");
+                    }
+                });
+        size = APIMetrics.newGauge(factory.createMetricName("Size"),
+                new Gauge<Long>() {
+                    public Long value() {
+                        return c.getLongValue("/cache_service/metrics/" + url
+                                + "/size");
+                    }
+                });
+        entries = APIMetrics.newGauge(factory.createMetricName("Entries"),
+                new Gauge<Integer>() {
+                    public Integer value() {
+                        return c.getIntValue("/cache_service/metrics/" + url
+                                + "/entries");
+                    }
+                });
+    }
+
+    // for backward compatibility
+    @Deprecated
+    public double getRecentHitRate() {
+        return 0;
+    }
+}