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.utils.memory;
  
  import org.apache.cassandra.utils.concurrent.Future;
  
  /**
   * The cleaner is used by {@link MemtableCleanerThread} in order to reclaim space from memtables, normally
   * by flushing the largest memtable.
   */
  public interface MemtableCleaner
  {
      /**
       * This is a function that schedules a cleaning task, normally flushing of the largest sstable.
       * The future will complete once the operation has completed and it will have a value set to true if
       * the cleaner was able to execute the cleaning operation or if another thread concurrently executed
       * the same clean operation. If no operation was even attempted, for example because no memtable was
       * found, then the value will be false.
       *
       * The future will complete with an error if the cleaning operation encounters an error.
       *
       */
      Future<Boolean> clean();
  }