content: /*
   * 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.function.DoubleSupplier;
  
  import com.google.common.annotations.VisibleForTesting;
  
  import com.codahale.metrics.Gauge;
  import com.codahale.metrics.Meter;
  import com.codahale.metrics.RatioGauge;
  
  import static org.apache.cassandra.metrics.CassandraMetricsRegistry.Metrics;
  
  /**
   * Base class for metrics for weighted or unweighted caches.
   */
  public abstract class AbstractCacheMetrics
  {
      /**
       * Type of the cache, basically its name
       */
      public final String type;
  
      /**
       * Total number of cache hits
       */
      public final Meter hits;
      /**
       * Total number of cache misses
       */
      public final Meter misses;
      /**
       * Total number of cache requests
       */
      public final Meter requests;
  
      /**
       * all time cache hit rate
       */
      public final Gauge<Double> hitRate;
      /**
       * 1m hit rate
       */
      public final Gauge<Double> oneMinuteHitRate;
      /**
       * 5m hit rate
       */
      public final Gauge<Double> fiveMinuteHitRate;
      /**
       * 15m hit rate
       */
      public final Gauge<Double> fifteenMinuteHitRate;
  
      protected final MetricNameFactory factory;
  
      protected AbstractCacheMetrics(MetricNameFactory metricNameFactory, String type)
      {
          this.type = type;
          factory = metricNameFactory;
          hits = Metrics.meter(factory.createMetricName("Hits"));
          misses = Metrics.meter(factory.createMetricName("Misses"));
          requests = Metrics.meter(factory.createMetricName("Requests"));
  
          hitRate = Metrics.register(factory.createMetricName("HitRate"),
                                     ratioGauge(hits::getCount, requests::getCount));
          oneMinuteHitRate = Metrics.register(factory.createMetricName("OneMinuteHitRate"),
                                              ratioGauge(hits::getOneMinuteRate, requests::getOneMinuteRate));
          fiveMinuteHitRate = Metrics.register(factory.createMetricName("FiveMinuteHitRate"),
                                               ratioGauge(hits::getFiveMinuteRate, requests::getFiveMinuteRate));
          fifteenMinuteHitRate = Metrics.register(factory.createMetricName("FifteenMinuteHitRate"),
                                                  ratioGauge(hits::getFifteenMinuteRate, requests::getFifteenMinuteRate));
      }
  
      @VisibleForTesting
      public void reset()
      {
          // No actual reset happens. The Meter counter is put to zero but will not reset the moving averages
          // It rather injects a weird value into them.
          // This method is being only used by CacheMetricsTest and CachingBench so fixing this issue was acknowledged
          // but not considered mandatory to be fixed now (CASSANDRA-16228)
          hits.mark(-hits.getCount());
          misses.mark(-misses.getCount());
          requests.mark(-requests.getCount());
      }
  
      private static RatioGauge ratioGauge(DoubleSupplier numeratorSupplier, DoubleSupplier denominatorSupplier)
      {
          return new RatioGauge()
          {
              @Override
              public Ratio getRatio()
              {
                  return Ratio.of(numeratorSupplier.getAsDouble(), denominatorSupplier.getAsDouble());
              }
          };
      }
  }
  