Review

10

/home/eko/MUBench/MUBench/mubench.pipeline/../checkouts/lucene/1918/original-src/org/apache/lucene/index/LogMergePolicy.java

findMerges(SegmentInfos)

class LogMergePolicy {
  /** Checks if any merges are now necessary and returns a
   *  {@link MergePolicy.MergeSpecification} if so.  A merge
   *  is necessary when there are more than {@link
   *  #setMergeFactor} segments at a given level.  When
   *  multiple levels have too many segments, this method
   *  will return multiple merges, allowing the {@link
   *  MergeScheduler} to use concurrency. */
  public MergeSpecification findMerges(SegmentInfos infos) throws IOException {

    final int numSegments = infos.size();
    if (verbose())
      message("findMerges: " + numSegments + " segments");

    // Compute levels, which is just log (base mergeFactor)
    // of the size of each segment
    float[] levels = new float[numSegments];
    final float norm = (float) Math.log(mergeFactor);

    for(int i=0;i<numSegments;i++) {
      final SegmentInfo info = infos.info(i);
      long size = size(info);

      // Floor tiny segments
      if (size < 1)
        size = 1;
      levels[i] = (float) Math.log(size)/norm;
    }

    final float levelFloor;
    if (minMergeSize <= 0)
      levelFloor = (float) 0.0;
    else
      levelFloor = (float) (Math.log(minMergeSize)/norm);

    // Now, we quantize the log values into levels.  The
    // first level is any segment whose log size is within
    // LEVEL_LOG_SPAN of the max size, or, who has such as
    // segment "to the right".  Then, we find the max of all
    // other segments and use that to define the next level
    // segment, etc.

    MergeSpecification spec = null;

    int start = 0;
    while(start < numSegments) {

      // Find max level of all segments not already
      // quantized.
      float maxLevel = levels[start];
      for(int i=1+start;i<numSegments;i++) {
        final float level = levels[i];
        if (level > maxLevel)
          maxLevel = level;
      }

      // Now search backwards for the rightmost segment that
      // falls into this level:
      float levelBottom;
      if (maxLevel < levelFloor)
        // All remaining segments fall into the min level
        levelBottom = -1.0F;
      else {
        levelBottom = (float) (maxLevel - LEVEL_LOG_SPAN);

        // Force a boundary at the level floor
        if (levelBottom < levelFloor && maxLevel >= levelFloor)
          levelBottom = levelFloor;
      }

      int upto = numSegments-1;
      while(upto >= start) {
        if (levels[upto] >= levelBottom) {
          break;
        }
        upto--;
      }
      if (verbose())
        message("  level " + levelBottom + " to " + maxLevel + ": " + (1+upto-start) + " segments");

      // Finally, record all merges that are viable at this level:
      int end = start + mergeFactor;
      while(end <= 1+upto) {
        boolean anyTooLarge = false;
        for(int i=start;i<end;i++) {
          final SegmentInfo info = infos.info(i);
          anyTooLarge |= (size(info) >= maxMergeSize || sizeDocs(info) >= maxMergeDocs);
        }

        if (!anyTooLarge) {
          if (spec == null)
            spec = new MergeSpecification();
          if (verbose())
            message("    " + start + " to " + end + ": add this merge");
          spec.add(new OneMerge(infos.range(start, end), useCompoundFile));
        } else if (verbose())
          message("    " + start + " to " + end + ": contains segment over maxMergeSize or maxMergeDocs; skipping");

        start = end;
        end = start + mergeFactor;
      }

      start = 1+upto;
    }

    return spec;
  }

}