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.bifromq.basekv.localengine;
  
  import java.util.Optional;
  
  /**
   * KV space supports checkpoint.
   */
  public interface ICPableKVSpace extends IKVSpace {
      /**
       * Make a checkpoint of the current range state.
       *
       * @return global unique id of the checkpoint
       */
      String checkpoint();
  
      /**
       * Open a readonly range object to access the checkpoint state. When the returned range object is garbage-collected
       * the associated checkpoint will be cleaned as well, except for the latest checkpoint. So the caller should keep a
       * strong reference to the checkpoint if it's still useful.
       *
       * @param checkpointId the checkpoint id
       * @return the range object for accessing the checkpoint
       */
      Optional<IKVSpaceCheckpoint> openCheckpoint(String checkpointId);
  }
  