/*
 * 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
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package org.apache.lucene.index;

import java.io.IOException;


An interface for implementations that support 2-phase commit. You can use TwoPhaseCommitTool to execute a 2-phase commit algorithm over several TwoPhaseCommits. 
@lucene.experimental
/**
 * An interface for implementations that support 2-phase commit. You can use
 * {@link TwoPhaseCommitTool} to execute a 2-phase commit algorithm over several
 * {@link TwoPhaseCommit}s.
 * 
 * @lucene.experimental
 */
public interface TwoPhaseCommit {

  
The first stage of a 2-phase commit. Implementations should do as much work as possible in this method, but avoid actual committing changes. If the 2-phase commit fails, rollback() is called to discard all changes since last successful commit. /**
   * The first stage of a 2-phase commit. Implementations should do as much work
   * as possible in this method, but avoid actual committing changes. If the
   * 2-phase commit fails, {@link #rollback()} is called to discard all changes
   * since last successful commit.
   */
  public long prepareCommit() throws IOException;

  
The second phase of a 2-phase commit. Implementations should ideally do very little work in this method (following prepareCommit(), and after it returns, the caller can assume that the changes were successfully committed to the underlying storage. /**
   * The second phase of a 2-phase commit. Implementations should ideally do
   * very little work in this method (following {@link #prepareCommit()}, and
   * after it returns, the caller can assume that the changes were successfully
   * committed to the underlying storage.
   */
  public long commit() throws IOException;

  
Discards any changes that have occurred since the last commit. In a 2-phase commit algorithm, where one of the objects failed to commit() or prepareCommit(), this method is used to roll all other objects back to their previous state. /**
   * Discards any changes that have occurred since the last commit. In a 2-phase
   * commit algorithm, where one of the objects failed to {@link #commit()} or
   * {@link #prepareCommit()}, this method is used to roll all other objects
   * back to their previous state.
   */
  public void rollback() throws IOException;
}