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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.

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/*
 * 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.
 */
package org.apache.cassandra.metrics;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;

import com.yammer.metrics.Metrics;
import com.yammer.metrics.core.Gauge;
import com.yammer.metrics.core.Meter;
import com.yammer.metrics.util.RatioGauge;

import org.apache.cassandra.cache.ICache;

/**
 * Metrics for {@code ICache}.
 */
public class CacheMetrics
{
    /** Cache capacity in bytes */
    public final Gauge 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 hitRate;
    /** Total size of cache, in bytes */
    public final Gauge size;
    /** Total number of cache entries */
    public final Gauge entries;

    private final AtomicLong lastRequests = new AtomicLong(0);
    private final AtomicLong lastHits = new AtomicLong(0);

    /**
     * Create metrics for given cache.
     *
     * @param type Type of Cache to identify metrics.
     * @param cache Cache to measure metrics
     */
    public CacheMetrics(String type, final ICache cache)
    {
        MetricNameFactory factory = new DefaultNameFactory("Cache", type);

        capacity = Metrics.newGauge(factory.createMetricName("Capacity"), new Gauge()
        {
            public Long value()
            {
                return cache.capacity();
            }
        });
        hits = Metrics.newMeter(factory.createMetricName("Hits"), "hits", TimeUnit.SECONDS);
        requests = Metrics.newMeter(factory.createMetricName("Requests"), "requests", TimeUnit.SECONDS);
        hitRate = Metrics.newGauge(factory.createMetricName("HitRate"), new RatioGauge()
        {
            protected double getNumerator()
            {
                return hits.count();
            }

            protected double getDenominator()
            {
                return requests.count();
            }
        });
        size = Metrics.newGauge(factory.createMetricName("Size"), new Gauge()
        {
            public Long value()
            {
                return cache.weightedSize();
            }
        });
        entries = Metrics.newGauge(factory.createMetricName("Entries"), new Gauge()
        {
            public Integer value()
            {
                return cache.size();
            }
        });
    }

    // for backward compatibility
    @Deprecated
    public double getRecentHitRate()
    {
        long r = requests.count();
        long h = hits.count();
        try
        {
            return ((double)(h - lastHits.get())) / (r - lastRequests.get());
        }
        finally
        {
            lastRequests.set(r);
            lastHits.set(h);
        }
    }
}