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.io.sstable.keycache;
  
  import java.util.Arrays;
  import java.util.List;
  
  import org.apache.cassandra.io.sstable.AbstractMetricsProviders;
  import org.apache.cassandra.io.sstable.GaugeProvider;
  import org.apache.cassandra.io.sstable.format.SSTableReader;
  
  public class KeyCacheMetrics<R extends SSTableReader & KeyCacheSupport<R>> extends AbstractMetricsProviders<R>
  {
      public final static KeyCacheMetrics<?> instance = new KeyCacheMetrics<>();
  
      @Override
      protected R map(SSTableReader r)
      {
          if (r instanceof KeyCacheSupport<?>)
              return (R) r;
          return null;
      }
  
      /** Key cache hit rate  for this CF */
      private final GaugeProvider<Double> keyCacheHitRate = newGaugeProvider("KeyCacheHitRate", readers -> {
          long hits = 0L;
          long requests = 0L;
          for (R sstable : readers)
          {
              hits += sstable.getKeyCache().getHits();
              requests += sstable.getKeyCache().getRequests();
          }
  
          return (double) hits / (double) Math.max(1, requests);
      });
  
      private final List<GaugeProvider<?>> gaugeProviders = Arrays.asList(keyCacheHitRate);
  
      public List<GaugeProvider<?>> getGaugeProviders()
      {
          return gaugeProviders;
      }
  }
  