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/*
* 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.lucene.index;
import java.io.IOException;
import java.util.List;
/**
* Expert: policy for deletion of stale {@link IndexCommit index commits}.
*
* Implement this interface, and set it on {@link
* IndexWriterConfig#setIndexDeletionPolicy(IndexDeletionPolicy)} to customize when older {@link
* IndexCommit point-in-time commits} are deleted from the index directory.
*
*
The default deletion policy is {@link KeepOnlyLastCommitDeletionPolicy}, always removes old
* commits as soon as a new commit is done (this matches the behavior before 2.2).
*
*
One expected use case for this (and the reason why it was first created) is to work around
* problems with an index directory accessed via filesystems like NFS because NFS does not provide
* the "delete on last close" semantics that Lucene's "point in time" search normally relies on. By
* implementing a custom deletion policy, such as "a commit is only removed once it has been stale
* for more than X minutes", you can give your readers time to refresh to the new commit before
* {@link IndexWriter} removes the old commits. Note that doing so will increase the storage
* requirements of the index. See LUCENE-710 for details.
*/
public abstract class IndexDeletionPolicy {
/** Sole constructor, typically called by sub-classes constructors. */
protected IndexDeletionPolicy() {}
/**
* This is called once when a writer is first instantiated to give the policy a chance to remove
* old commit points.
*
*
The writer locates all index commits present in the index directory and calls this method.
* The policy may choose to delete some of the commit points, doing so by calling method {@link
* IndexCommit#delete delete()} of {@link IndexCommit}.
*
*
Note: the last CommitPoint is the most recent one, i.e. the "front index state". Be
* careful not to delete it, unless you know for sure what you are doing, and unless you can
* afford to lose the index content while doing that.
*
* @param commits List of current {@link IndexCommit point-in-time commits}, sorted by age (the
* 0th one is the oldest commit). Note that for a new index this method is invoked with an
* empty list.
*/
public abstract void onInit(List commits) throws IOException;
/**
* This is called each time the writer completed a commit. This gives the policy a chance to
* remove old commit points with each commit.
*
*
The policy may now choose to delete old commit points by calling method {@link
* IndexCommit#delete delete()} of {@link IndexCommit}.
*
*
This method is only called when {@link IndexWriter#commit} or {@link IndexWriter#close} is
* called, or possibly not at all if the {@link IndexWriter#rollback} is called.
*
*
Note: the last CommitPoint is the most recent one, i.e. the "front index state". Be
* careful not to delete it, unless you know for sure what you are doing, and unless you can
* afford to lose the index content while doing that.
*
* @param commits List of {@link IndexCommit}, sorted by age (the 0th one is the oldest commit).
*/
public abstract void onCommit(List commits) throws IOException;
}