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Lucene example source code file (MergePolicy.java)

This example Lucene source code file (MergePolicy.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

corruptindexexception, directory, directory, indexwriter, indexwriter, io, ioexception, ioexception, list, mergeabortedexception, mergeabortedexception, mergeexception, mergespecification, segmentinfo, stringbuilder, util

The Lucene MergePolicy.java source code

package org.apache.lucene.index;

/**
 * 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.
 */

import org.apache.lucene.store.Directory;
import org.apache.lucene.util.SetOnce;
import org.apache.lucene.util.SetOnce.AlreadySetException;

import java.io.IOException;
import java.util.List;
import java.util.ArrayList;
import java.util.Map;

/**
 * <p>Expert: a MergePolicy determines the sequence of
 * primitive merge operations to be used for overall merge
 * and optimize operations.</p>
 * 
 * <p>Whenever the segments in an index have been altered by
 * {@link IndexWriter}, either the addition of a newly
 * flushed segment, addition of many segments from
 * addIndexes* calls, or a previous merge that may now need
 * to cascade, {@link IndexWriter} invokes {@link
 * #findMerges} to give the MergePolicy a chance to pick
 * merges that are now required.  This method returns a
 * {@link MergeSpecification} instance describing the set of
 * merges that should be done, or null if no merges are
 * necessary.  When IndexWriter.optimize is called, it calls
 * {@link #findMergesForOptimize} and the MergePolicy should
 * then return the necessary merges.</p>
 *
 * <p>Note that the policy can return more than one merge at
 * a time.  In this case, if the writer is using {@link
 * SerialMergeScheduler}, the merges will be run
 * sequentially but if it is using {@link
 * ConcurrentMergeScheduler} they will be run concurrently.</p>
 * 
 * <p>The default MergePolicy is {@link
 * TieredMergePolicy}.</p>
 *
 * @lucene.experimental
 */

public abstract class MergePolicy implements java.io.Closeable {

  /** OneMerge provides the information necessary to perform
   *  an individual primitive merge operation, resulting in
   *  a single new segment.  The merge spec includes the
   *  subset of segments to be merged as well as whether the
   *  new segment should use the compound file format. */

  public static class OneMerge {

    SegmentInfo info;               // used by IndexWriter
    boolean optimize;               // used by IndexWriter
    boolean registerDone;           // used by IndexWriter
    long mergeGen;                  // used by IndexWriter
    boolean isExternal;             // used by IndexWriter
    int maxNumSegmentsOptimize;     // used by IndexWriter
    public long estimatedMergeBytes;       // used by IndexWriter
    List<SegmentReader> readers;        // used by IndexWriter
    List<SegmentReader> readerClones;   // used by IndexWriter
    public final List<SegmentInfo> segments;
    public final int totalDocCount;
    boolean aborted;
    Throwable error;
    boolean paused;

    public OneMerge(List<SegmentInfo> segments) {
      if (0 == segments.size())
        throw new RuntimeException("segments must include at least one segment");
      // clone the list, as the in list may be based off original SegmentInfos and may be modified
      this.segments = new ArrayList<SegmentInfo>(segments);
      int count = 0;
      for(SegmentInfo info : segments) {
        count += info.docCount;
      }
      totalDocCount = count;
    }

    /** Record that an exception occurred while executing
     *  this merge */
    synchronized void setException(Throwable error) {
      this.error = error;
    }

    /** Retrieve previous exception set by {@link
     *  #setException}. */
    synchronized Throwable getException() {
      return error;
    }

    /** Mark this merge as aborted.  If this is called
     *  before the merge is committed then the merge will
     *  not be committed. */
    synchronized void abort() {
      aborted = true;
      notifyAll();
    }

    /** Returns true if this merge was aborted. */
    synchronized boolean isAborted() {
      return aborted;
    }

    synchronized void checkAborted(Directory dir) throws MergeAbortedException {
      if (aborted) {
        throw new MergeAbortedException("merge is aborted: " + segString(dir));
      }

      while (paused) {
        try {
          // In theory we could wait() indefinitely, but we
          // do 1000 msec, defensively
          wait(1000);
        } catch (InterruptedException ie) {
          throw new RuntimeException(ie);
        }
        if (aborted) {
          throw new MergeAbortedException("merge is aborted: " + segString(dir));
        }
      }
    }

    synchronized public void setPause(boolean paused) {
      this.paused = paused;
      if (!paused) {
        // Wakeup merge thread, if it's waiting
        notifyAll();
      }
    }

    synchronized public boolean getPause() {
      return paused;
    }

    public String segString(Directory dir) {
      StringBuilder b = new StringBuilder();
      final int numSegments = segments.size();
      for(int i=0;i<numSegments;i++) {
        if (i > 0) b.append(' ');
        b.append(segments.get(i).toString(dir, 0));
      }
      if (info != null)
        b.append(" into ").append(info.name);
      if (optimize)
        b.append(" [optimize]");
      if (aborted) {
        b.append(" [ABORTED]");
      }
      return b.toString();
    }
    
    /**
     * Returns the total size in bytes of this merge. Note that this does not
     * indicate the size of the merged segment, but the input total size.
     * */
    public long totalBytesSize() throws IOException {
      long total = 0;
      for (SegmentInfo info : segments) {
        total += info.sizeInBytes(true);
      }
      return total;
    }

    /**
     * Returns the total number of documents that are included with this merge.
     * Note that this does not indicate the number of documents after the merge.
     * */
    public int totalNumDocs() throws IOException {
      int total = 0;
      for (SegmentInfo info : segments) {
        total += info.docCount;
      }
      return total;
    }
  }

  /**
   * A MergeSpecification instance provides the information
   * necessary to perform multiple merges.  It simply
   * contains a list of {@link OneMerge} instances.
   */

  public static class MergeSpecification {

    /**
     * The subset of segments to be included in the primitive merge.
     */

    public final List<OneMerge> merges = new ArrayList();

    public void add(OneMerge merge) {
      merges.add(merge);
    }

    public String segString(Directory dir) {
      StringBuilder b = new StringBuilder();
      b.append("MergeSpec:\n");
      final int count = merges.size();
      for(int i=0;i<count;i++)
        b.append("  ").append(1 + i).append(": ").append(merges.get(i).segString(dir));
      return b.toString();
    }
  }

  /** Exception thrown if there are any problems while
   *  executing a merge. */
  public static class MergeException extends RuntimeException {
    private Directory dir;

    public MergeException(String message, Directory dir) {
      super(message);
      this.dir = dir;
    }

    public MergeException(Throwable exc, Directory dir) {
      super(exc);
      this.dir = dir;
    }
    /** Returns the {@link Directory} of the index that hit
     *  the exception. */
    public Directory getDirectory() {
      return dir;
    }
  }

  public static class MergeAbortedException extends IOException {
    public MergeAbortedException() {
      super("merge is aborted");
    }
    public MergeAbortedException(String message) {
      super(message);
    }
  }

  protected final SetOnce<IndexWriter> writer;

  /**
   * Creates a new merge policy instance. Note that if you intend to use it
   * without passing it to {@link IndexWriter}, you should call
   * {@link #setIndexWriter(IndexWriter)}.
   */
  public MergePolicy() {
    writer = new SetOnce<IndexWriter>();
  }

  /**
   * Sets the {@link IndexWriter} to use by this merge policy. This method is
   * allowed to be called only once, and is usually set by IndexWriter. If it is
   * called more than once, {@link AlreadySetException} is thrown.
   * 
   * @see SetOnce
   */
  public void setIndexWriter(IndexWriter writer) {
    this.writer.set(writer);
  }
  
  /**
   * Determine what set of merge operations are now necessary on the index.
   * {@link IndexWriter} calls this whenever there is a change to the segments.
   * This call is always synchronized on the {@link IndexWriter} instance so
   * only one thread at a time will call this method.
   * 
   * @param segmentInfos
   *          the total set of segments in the index
   */
  public abstract MergeSpecification findMerges(SegmentInfos segmentInfos)
      throws CorruptIndexException, IOException;

  /**
   * Determine what set of merge operations is necessary in order to optimize
   * the index. {@link IndexWriter} calls this when its
   * {@link IndexWriter#optimize()} method is called. This call is always
   * synchronized on the {@link IndexWriter} instance so only one thread at a
   * time will call this method.
   * 
   * @param segmentInfos
   *          the total set of segments in the index
   * @param maxSegmentCount
   *          requested maximum number of segments in the index (currently this
   *          is always 1)
   * @param segmentsToOptimize
   *          contains the specific SegmentInfo instances that must be merged
   *          away. This may be a subset of all
   *          SegmentInfos.  If the value is True for a
   *          given SegmentInfo, that means this segment was
   *          an original segment present in the
   *          to-be-optimized index; else, it was a segment
   *          produced by a cascaded merge.
   */
  public abstract MergeSpecification findMergesForOptimize(
          SegmentInfos segmentInfos, int maxSegmentCount, Map<SegmentInfo,Boolean> segmentsToOptimize)
      throws CorruptIndexException, IOException;

  /**
   * Determine what set of merge operations is necessary in order to expunge all
   * deletes from the index.
   * 
   * @param segmentInfos
   *          the total set of segments in the index
   */
  public abstract MergeSpecification findMergesToExpungeDeletes(
      SegmentInfos segmentInfos) throws CorruptIndexException, IOException;

  /**
   * Release all resources for the policy.
   */
  public abstract void close();

  /** Returns true if a new segment (regardless of its origin) should use the compound file format. */
  public abstract boolean useCompoundFile(SegmentInfos segments, SegmentInfo newSegment) throws IOException;
}

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