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.concurrent.atomic.LongAdder;
  import javax.annotation.Nonnull;
  import javax.annotation.Nullable;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import org.apache.cassandra.cache.InstrumentingCache;
  import org.apache.cassandra.cache.KeyCacheKey;
  import org.apache.cassandra.io.sstable.AbstractRowIndexEntry;
  
  /**
   * A simple wrapper of possibly global cache with local metrics.
   */
  public class KeyCache
  {
      public static final KeyCache NO_CACHE = new KeyCache(null);
  
      private final static Logger logger = LoggerFactory.getLogger(KeyCache.class);
  
      private final InstrumentingCache<KeyCacheKey, AbstractRowIndexEntry> cache;
      private final LongAdder hits = new LongAdder();
      private final LongAdder requests = new LongAdder();
  
      public KeyCache(@Nullable InstrumentingCache<KeyCacheKey, AbstractRowIndexEntry> cache)
      {
          this.cache = cache;
      }
  
      public long getHits()
      {
          return cache != null ? hits.sum() : 0;
      }
  
      public long getRequests()
      {
          return cache != null ? requests.sum() : 0;
      }
  
      public void put(@Nonnull KeyCacheKey cacheKey, @Nonnull AbstractRowIndexEntry info)
      {
          if (cache == null)
              return;
  
          logger.trace("Adding cache entry for {} -> {}", cacheKey, info);
          cache.put(cacheKey, info);
      }
  
      public @Nullable AbstractRowIndexEntry get(KeyCacheKey key, boolean updateStats)
      {
          if (cache == null)
              return null;
  
          if (updateStats)
          {
              requests.increment();
              AbstractRowIndexEntry r = cache.get(key);
              if (r != null)
                  hits.increment();
              return r;
          }
          else
          {
              return cache.getInternal(key);
          }
      }
  
      public boolean isEnabled()
      {
          return cache != null;
      }
  }
  