segmentinfos.java

Lucene a java open-source SearchEngine Framework

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.store.IndexInput;
import org.apache.lucene.store.IndexOutput;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintStream;
import java.util.Vector;

final class SegmentInfos extends Vector {
  
  
  /** The file format version, a negative number. */
  /* Works since counter, the old 1st entry, is always >= 0 */
  public static final int FORMAT = -1;

  /** This format adds details used for lockless commits.  It differs
   * slightly from the previous format in that file names
   * are never re-used (write once).  Instead, each file is
   * written to the next generation.  For example,
   * segments_1, segments_2, etc.  This allows us to not use
   * a commit lock.  See <a
   * href="http://lucene.apache.org/java/docs/fileformats.html">file
   * formats</a> for details.
   */
  public static final int FORMAT_LOCKLESS = -2;

  /** This format adds a "hasSingleNormFile" flag into each segment info.
   * See <a href="http://issues.apache.org/jira/browse/LUCENE-756">LUCENE-756</a>
   * for details.
   */
  public static final int FORMAT_SINGLE_NORM_FILE = -3;

  /** This format allows multiple segments to share a single
   * vectors and stored fields file. */
  public static final int FORMAT_SHARED_DOC_STORE = -4;

  /* This must always point to the most recent file format. */
  private static final int CURRENT_FORMAT = FORMAT_SHARED_DOC_STORE;
  
  public int counter = 0;    // used to name new segments
  /**
   * counts how often the index has been changed by adding or deleting docs.
   * starting with the current time in milliseconds forces to create unique version numbers.
   */
  private long version = System.currentTimeMillis();

  private long generation = 0;     // generation of the "segments_N" for the next commit
  private long lastGeneration = 0; // generation of the "segments_N" file we last successfully read
                                   // or wrote; this is normally the same as generation except if
                                   // there was an IOException that had interrupted a commit

  /**
   * If non-null, information about loading segments_N files
   * will be printed here.  @see #setInfoStream.
   */
  private static PrintStream infoStream;

  public final SegmentInfo info(int i) {
    return (SegmentInfo) elementAt(i);
  }

  /**
   * Get the generation (N) of the current segments_N file
   * from a list of files.
   *
   * @param files -- array of file names to check
   */
  public static long getCurrentSegmentGeneration(String[] files) {
    if (files == null) {
      return -1;
    }
    long max = -1;
    for (int i = 0; i < files.length; i++) {
      String file = files[i];
      if (file.startsWith(IndexFileNames.SEGMENTS) && !file.equals(IndexFileNames.SEGMENTS_GEN)) {
        long gen = generationFromSegmentsFileName(file);
        if (gen > max) {
          max = gen;
        }
      }
    }
    return max;
  }

  /**
   * Get the generation (N) of the current segments_N file
   * in the directory.
   *
   * @param directory -- directory to search for the latest segments_N file
   */
  public static long getCurrentSegmentGeneration(Directory directory) throws IOException {
    String[] files = directory.list();
    if (files == null)
      throw new IOException("cannot read directory " + directory + ": list() returned null");
    return getCurrentSegmentGeneration(files);
  }

  /**
   * Get the filename of the current segments_N file
   * from a list of files.
   *
   * @param files -- array of file names to check
   */

  public static String getCurrentSegmentFileName(String[] files) throws IOException {
    return IndexFileNames.fileNameFromGeneration(IndexFileNames.SEGMENTS,
                                                 "",
                                                 getCurrentSegmentGeneration(files));
  }

  /**
   * Get the filename of the current segments_N file
   * in the directory.
   *
   * @param directory -- directory to search for the latest segments_N file
   */
  public static String getCurrentSegmentFileName(Directory directory) throws IOException {
    return IndexFileNames.fileNameFromGeneration(IndexFileNames.SEGMENTS,
                                                 "",
                                                 getCurrentSegmentGeneration(directory));
  }

  /**
   * Get the segments_N filename in use by this segment infos.
   */
  public String getCurrentSegmentFileName() {
    return IndexFileNames.fileNameFromGeneration(IndexFileNames.SEGMENTS,
                                                 "",
                                                 lastGeneration);
  }

  /**
   * Parse the generation off the segments file name and
   * return it.
   */
  public static long generationFromSegmentsFileName(String fileName) {
    if (fileName.equals(IndexFileNames.SEGMENTS)) {
      return 0;
    } else if (fileName.startsWith(IndexFileNames.SEGMENTS)) {
      return Long.parseLong(fileName.substring(1+IndexFileNames.SEGMENTS.length()),
                            Character.MAX_RADIX);
    } else {
      throw new IllegalArgumentException("fileName \"" + fileName + "\" is not a segments file");
    }
  }


  /**
   * Get the next segments_N filename that will be written.
   */
  public String getNextSegmentFileName() {
    long nextGeneration;

    if (generation == -1) {
      nextGeneration = 1;
    } else {
      nextGeneration = generation+1;
    }
    return IndexFileNames.fileNameFromGeneration(IndexFileNames.SEGMENTS,
                                                 "",
                                                 nextGeneration);
  }

  /**
   * Read a particular segmentFileName.  Note that this may
   * throw an IOException if a commit is in process.
   *
   * @param directory -- directory containing the segments file
   * @param segmentFileName -- segment file to load
   * @throws CorruptIndexException if the index is corrupt
   * @throws IOException if there is a low-level IO error
   */
  public final void read(Directory directory, String segmentFileName) throws CorruptIndexException, IOException {
    boolean success = false;

    // Clear any previous segments:
    clear();

    IndexInput input = directory.openInput(segmentFileName);

    generation = generationFromSegmentsFileName(segmentFileName);

    lastGeneration = generation;

    try {
      int format = input.readInt();
      if(format < 0){     // file contains explicit format info
        // check that it is a format we can understand
        if (format < CURRENT_FORMAT)
          throw new CorruptIndexException("Unknown format version: " + format);
        version = input.readLong(); // read version
        counter = input.readInt(); // read counter
      }
      else{     // file is in old format without explicit format info
        counter = format;
      }
      
      for (int i = input.readInt(); i > 0; i--) { // read segmentInfos
        addElement(new SegmentInfo(directory, format, input));
      }
      
      if(format >= 0){    // in old format the version number may be at the end of the file
        if (input.getFilePointer() >= input.length())
          version = System.currentTimeMillis(); // old file format without version number
        else
          version = input.readLong(); // read version
      }
      success = true;
    }
    finally {
      input.close();
      if (!success) {
        // Clear any segment infos we had loaded so we
        // have a clean slate on retry:
        clear();
      }
    }
  }

  /**
   * This version of read uses the retry logic (for lock-less
   * commits) to find the right segments file to load.
   * @throws CorruptIndexException if the index is corrupt
   * @throws IOException if there is a low-level IO error
   */
  public final void read(Directory directory) throws CorruptIndexException, IOException {

    generation = lastGeneration = -1;

    new FindSegmentsFile(directory) {

      protected Object doBody(String segmentFileName) throws CorruptIndexException, IOException {
        read(directory, segmentFileName);
        return null;
      }
    }.run();
  }

  public final void write(Directory directory) throws IOException {

    String segmentFileName = getNextSegmentFileName();

    // Always advance the generation on write:
    if (generation == -1) {
      generation = 1;
    } else {
      generation++;
    }

    IndexOutput output = directory.createOutput(segmentFileName);

    boolean success = false;

    try {
      output.writeInt(CURRENT_FORMAT); // write FORMAT
      output.writeLong(++version); // every write changes
                                   // the index
      output.writeInt(counter); // write counter
      output.writeInt(size()); // write infos
      for (int i = 0; i < size(); i++) {
        info(i).write(output);
      }         
    }
    finally {
      try {
        output.close();
        success = true;
      } finally {
        if (!success) {
          // Try not to leave a truncated segments_N file in
          // the index:
          directory.deleteFile(segmentFileName);
        }
      }
    }

    try {
      output = directory.createOutput(IndexFileNames.SEGMENTS_GEN);
      try {
        output.writeInt(FORMAT_LOCKLESS);
        output.writeLong(generation);
        output.writeLong(generation);
      } finally {
        output.close();
      }
    } catch (IOException e) {
      // It's OK if we fail to write this file since it's
      // used only as one of the retry fallbacks.
    }
    
    lastGeneration = generation;
  }

  /**
   * Returns a copy of this instance, also copying each
   * SegmentInfo.
   */
  
  public Object clone() {
    SegmentInfos sis = (SegmentInfos) super.clone();
    for(int i=0;i<sis.size();i++) {
      sis.setElementAt(((SegmentInfo) sis.elementAt(i)).clone(), i);
    }
    return sis;
  }

  /**
   * version number when this SegmentInfos was generated.
   */
  public long getVersion() {
    return version;
  }
  public long getGeneration() {
    return generation;
  }
  public long getLastGeneration() {
    return lastGeneration;
  }

  /**
   * Current version number from segments file.
   * @throws CorruptIndexException if the index is corrupt
   * @throws IOException if there is a low-level IO error
   */
  public static long readCurrentVersion(Directory directory)
    throws CorruptIndexException, IOException {

    return ((Long) new FindSegmentsFile(directory) {
        protected Object doBody(String segmentFileName) throws CorruptIndexException, IOException {

          IndexInput input = directory.openInput(segmentFileName);