hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/utils/db/cache/TableCache.java

/*
 * 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.hadoop.hdds.utils.db.cache;

import org.apache.hadoop.classification.InterfaceAudience.Private;
import org.apache.hadoop.classification.InterfaceStability.Evolving;

import java.util.Iterator;
import java.util.Map;

/**
 * Cache used for RocksDB tables.
 * @param <CACHEKEY>
 * @param <CACHEVALUE>
 */

@Private
@Evolving
public interface TableCache<CACHEKEY extends CacheKey,
    CACHEVALUE extends CacheValue> {

  /**
   * Return the value for the key if it is present, otherwise return null.
   * @param cacheKey
   * @return CACHEVALUE
   */
  CACHEVALUE get(CACHEKEY cacheKey);

  /**
   * This method should be called for tables with cache cleanup policy
   * {@link TableCacheImpl.CacheCleanupPolicy#NEVER} after system restart to
   * fill up the cache.
   * @param cacheKey
   * @param cacheValue
   */
  void loadInitial(CACHEKEY cacheKey, CACHEVALUE cacheValue);

  /**
   * Add an entry to the cache, if the key already exists it overrides.
   * @param cacheKey
   * @param value
   */
  void put(CACHEKEY cacheKey, CACHEVALUE value);

  /**
   * Removes all the entries from the cache which are having epoch value less
   * than or equal to specified epoch value.
   *
   * If clean up policy is NEVER, this is a do nothing operation.
   * If clean up policy is MANUAL, it is caller responsibility to cleanup the
   * cache before calling cleanup.
   * @param epoch
   */
  void cleanup(long epoch);

  /**
   * Return the size of the cache.
   * @return size
   */
  int size();

  /**
   * Return an iterator for the cache.
   * @return iterator of the underlying cache for the table.
   */
  Iterator<Map.Entry<CACHEKEY, CACHEVALUE>> iterator();

  /**
   * Check key exist in cache or not.
   *
   * If it exists return CacheResult with value and status as
   * {@link CacheResult.CacheStatus#EXISTS}
   *
   * If it does not exist:
   *  If cache clean up policy is
   *  {@link TableCacheImpl.CacheCleanupPolicy#NEVER} it means table cache is
   *  full cache. It return's {@link CacheResult} with null
   *  and status as {@link CacheResult.CacheStatus#NOT_EXIST}.
   *
   *  If cache clean up policy is
   *  {@link TableCacheImpl.CacheCleanupPolicy#MANUAL} it means
   *  table cache is partial cache. It return's {@link CacheResult} with
   *  null and status as MAY_EXIST.
   *
   * @param cachekey
   */
  CacheResult<CACHEVALUE> lookup(CACHEKEY cachekey);

}