/*
* 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.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Locale;
import java.util.Map;
/**
* <p>This class implements a {@link MergePolicy} that tries
* to merge segments into levels of exponentially
* increasing size, where each level has fewer segments than
* the value of the merge factor. Whenever extra segments
* (beyond the merge factor upper bound) are encountered,
* all segments within the level are merged. You can get or
* set the merge factor using {@link #getMergeFactor()} and
* {@link #setMergeFactor(int)} respectively.</p>
*
* <p>This class is abstract and requires a subclass to
* define the {@link #size} method which specifies how a
* segment's size is determined. {@link LogDocMergePolicy}
* is one subclass that measures size by document count in
* the segment. {@link LogByteSizeMergePolicy} is another
* subclass that measures size as the total byte size of the
* file(s) for the segment.</p>
*/
public abstract class LogMergePolicy extends MergePolicy {
/** Defines the allowed range of log(size) for each
* level. A level is computed by taking the max segment
* log size, minus LEVEL_LOG_SPAN, and finding all
* segments falling within that range. */
public static final double LEVEL_LOG_SPAN = 0.75;
/** Default merge factor, which is how many segments are
* merged at a time */
public static final int DEFAULT_MERGE_FACTOR = 10;
/** Default maximum segment size. A segment of this size
* or larger will never be merged. @see setMaxMergeDocs */
public static final int DEFAULT_MAX_MERGE_DOCS = Integer.MAX_VALUE;
/** Default noCFSRatio. If a merge's size is {@code >= 10%} of
* the index, then we disable compound file for it.
* @see MergePolicy#setNoCFSRatio */
public static final double DEFAULT_NO_CFS_RATIO = 0.1;
/** How many segments to merge at a time. */
protected int mergeFactor = DEFAULT_MERGE_FACTOR;
/** Any segments whose size is smaller than this value
* will be rounded up to this value. This ensures that
* tiny segments are aggressively merged. */
protected long minMergeSize;
/** If the size of a segment exceeds this value then it
* will never be merged. */
protected long maxMergeSize;
// Although the core MPs set it explicitly, we must default in case someone
// out there wrote his own LMP ...
/** If the size of a segment exceeds this value then it
* will never be merged during {@link IndexWriter#forceMerge}. */
protected long maxMergeSizeForForcedMerge = Long.MAX_VALUE;
/** If a segment has more than this many documents then it
* will never be merged. */
protected int maxMergeDocs = DEFAULT_MAX_MERGE_DOCS;
/** If true, we pro-rate a segment's size by the
* percentage of non-deleted documents. */
protected boolean calibrateSizeByDeletes = true;
/** Sole constructor. (For invocation by subclass
* constructors, typically implicit.) */
public LogMergePolicy() {
super(DEFAULT_NO_CFS_RATIO, MergePolicy.DEFAULT_MAX_CFS_SEGMENT_SIZE);
}
/** Returns true if {@code LMP} is enabled in {@link
* IndexWriter}'s {@code infoStream}. */
protected boolean verbose(IndexWriter writer) {
return writer != null && writer.infoStream.isEnabled("LMP");
}
/** Print a debug message to {@link IndexWriter}'s {@code
* infoStream}. */
protected void message(String message, IndexWriter writer) {
if (verbose(writer)) {
writer.infoStream.message("LMP", message);
}
}
/** <p>Returns the number of segments that are merged at
* once and also controls the total number of segments
* allowed to accumulate in the index.</p> */
public int getMergeFactor() {
return mergeFactor;
}
/** Determines how often segment indices are merged by
* addDocument(). With smaller values, less RAM is used
* while indexing, and searches are
* faster, but indexing speed is slower. With larger
* values, more RAM is used during indexing, and while
* searches is slower, indexing is
* faster. Thus larger values ({@code > 10}) are best for batch
* index creation, and smaller values ({@code < 10}) for indices
* that are interactively maintained. */
public void setMergeFactor(int mergeFactor) {
if (mergeFactor < 2)
throw new IllegalArgumentException("mergeFactor cannot be less than 2");
this.mergeFactor = mergeFactor;
}
/** Sets whether the segment size should be calibrated by
* the number of deletes when choosing segments for merge. */
public void setCalibrateSizeByDeletes(boolean calibrateSizeByDeletes) {
this.calibrateSizeByDeletes = calibrateSizeByDeletes;
}
/** Returns true if the segment size should be calibrated
* by the number of deletes when choosing segments for merge. */
public boolean getCalibrateSizeByDeletes() {
return calibrateSizeByDeletes;
}
/** Return the number of documents in the provided {@link
* SegmentCommitInfo}, pro-rated by percentage of
* non-deleted documents if {@link
* #setCalibrateSizeByDeletes} is set. */
protected long sizeDocs(SegmentCommitInfo info, IndexWriter writer) throws IOException {
if (calibrateSizeByDeletes) {
int delCount = writer.numDeletedDocs(info);
assert delCount <= info.info.maxDoc();
return (info.info.maxDoc() - (long)delCount);
} else {
return info.info.maxDoc();
}
}
/** Return the byte size of the provided {@link
* SegmentCommitInfo}, pro-rated by percentage of
* non-deleted documents if {@link
* #setCalibrateSizeByDeletes} is set. */
protected long sizeBytes(SegmentCommitInfo info, IndexWriter writer) throws IOException {
if (calibrateSizeByDeletes) {
return super.size(info, writer);
}
return info.sizeInBytes();
}
/** Returns true if the number of segments eligible for
* merging is less than or equal to the specified {@code
* maxNumSegments}. */
protected boolean isMerged(SegmentInfos infos, int maxNumSegments, Map<SegmentCommitInfo,Boolean> segmentsToMerge, IndexWriter writer) throws IOException {
final int numSegments = infos.size();
int numToMerge = 0;
SegmentCommitInfo mergeInfo = null;
boolean segmentIsOriginal = false;
for(int i=0;i<numSegments && numToMerge <= maxNumSegments;i++) {
final SegmentCommitInfo info = infos.info(i);
final Boolean isOriginal = segmentsToMerge.get(info);
if (isOriginal != null) {
segmentIsOriginal = isOriginal;
numToMerge++;
mergeInfo = info;
}
}
return numToMerge <= maxNumSegments &&
(numToMerge != 1 || !segmentIsOriginal || isMerged(infos, mergeInfo, writer));
}
/**
* Returns the merges necessary to merge the index, taking the max merge
* size or max merge docs into consideration. This method attempts to respect
* the {@code maxNumSegments} parameter, however it might be, due to size
* constraints, that more than that number of segments will remain in the
* index. Also, this method does not guarantee that exactly {@code
* maxNumSegments} will remain, but <= that number.
*/
private MergeSpecification findForcedMergesSizeLimit(
SegmentInfos infos, int maxNumSegments, int last, IndexWriter writer) throws IOException {
MergeSpecification spec = new MergeSpecification();
final List<SegmentCommitInfo> segments = infos.asList();
int start = last - 1;
while (start >= 0) {
SegmentCommitInfo info = infos.info(start);
if (size(info, writer) > maxMergeSizeForForcedMerge || sizeDocs(info, writer) > maxMergeDocs) {
if (verbose(writer)) {
message("findForcedMergesSizeLimit: skip segment=" + info + ": size is > maxMergeSize (" + maxMergeSizeForForcedMerge + ") or sizeDocs is > maxMergeDocs (" + maxMergeDocs + ")", writer);
}
// need to skip that segment + add a merge for the 'right' segments,
// unless there is only 1 which is merged.
if (last - start - 1 > 1 || (start != last - 1 && !isMerged(infos, infos.info(start + 1), writer))) {
// there is more than 1 segment to the right of
// this one, or a mergeable single segment.
spec.add(new OneMerge(segments.subList(start + 1, last)));
}
last = start;
} else if (last - start == mergeFactor) {
// mergeFactor eligible segments were found, add them as a merge.
spec.add(new OneMerge(segments.subList(start, last)));
last = start;
}
--start;
}
// Add any left-over segments, unless there is just 1
// already fully merged
if (last > 0 && (++start + 1 < last || !isMerged(infos, infos.info(start), writer))) {
spec.add(new OneMerge(segments.subList(start, last)));
}
return spec.merges.size() == 0 ? null : spec;
}
/**
* Returns the merges necessary to forceMerge the index. This method constraints
* the returned merges only by the {@code maxNumSegments} parameter, and
* guaranteed that exactly that number of segments will remain in the index.
*/
private MergeSpecification findForcedMergesMaxNumSegments(SegmentInfos infos, int maxNumSegments, int last, IndexWriter writer) throws IOException {
MergeSpecification spec = new MergeSpecification();
final List<SegmentCommitInfo> segments = infos.asList();
// First, enroll all "full" merges (size
// mergeFactor) to potentially be run concurrently:
while (last - maxNumSegments + 1 >= mergeFactor) {
spec.add(new OneMerge(segments.subList(last - mergeFactor, last)));
last -= mergeFactor;
}
// Only if there are no full merges pending do we
// add a final partial (< mergeFactor segments) merge:
if (0 == spec.merges.size()) {
if (maxNumSegments == 1) {
// Since we must merge down to 1 segment, the
// choice is simple:
if (last > 1 || !isMerged(infos, infos.info(0), writer)) {
spec.add(new OneMerge(segments.subList(0, last)));
}
} else if (last > maxNumSegments) {
// Take care to pick a partial merge that is
// least cost, but does not make the index too
// lopsided. If we always just picked the
// partial tail then we could produce a highly
// lopsided index over time:
// We must merge this many segments to leave
// maxNumSegments in the index (from when
// forceMerge was first kicked off):
final int finalMergeSize = last - maxNumSegments + 1;
// Consider all possible starting points:
long bestSize = 0;
int bestStart = 0;
for(int i=0;i<last-finalMergeSize+1;i++) {
long sumSize = 0;
for(int j=0;j<finalMergeSize;j++) {
sumSize += size(infos.info(j+i), writer);
}
if (i == 0 || (sumSize < 2*size(infos.info(i-1), writer) && sumSize < bestSize)) {
bestStart = i;
bestSize = sumSize;
}
}
spec.add(new OneMerge(segments.subList(bestStart, bestStart + finalMergeSize)));
}
}
return spec.merges.size() == 0 ? null : spec;
}
/** Returns the merges necessary to merge the index down
* to a specified number of segments.
* This respects the {@link #maxMergeSizeForForcedMerge} setting.
* By default, and assuming {@code maxNumSegments=1}, only
* one segment will be left in the index, where that segment
* has no deletions pending nor separate norms, and it is in
* compound file format if the current useCompoundFile
* setting is true. This method returns multiple merges
* (mergeFactor at a time) so the {@link MergeScheduler}
* in use may make use of concurrency. */
@Override
public MergeSpecification findForcedMerges(SegmentInfos infos,
int maxNumSegments, Map<SegmentCommitInfo,Boolean> segmentsToMerge, IndexWriter writer) throws IOException {
assert maxNumSegments > 0;
if (verbose(writer)) {
message("findForcedMerges: maxNumSegs=" + maxNumSegments + " segsToMerge="+ segmentsToMerge, writer);
}
// If the segments are already merged (e.g. there's only 1 segment), or
// there are <maxNumSegments:.
if (isMerged(infos, maxNumSegments, segmentsToMerge, writer)) {
if (verbose(writer)) {
message("already merged; skip", writer);
}
return null;
}
// Find the newest (rightmost) segment that needs to
// be merged (other segments may have been flushed
// since merging started):
int last = infos.size();
while (last > 0) {
final SegmentCommitInfo info = infos.info(--last);
if (segmentsToMerge.get(info) != null) {
last++;
break;
}
}
if (last == 0) {
if (verbose(writer)) {
message("last == 0; skip", writer);
}
return null;
}
// There is only one segment already, and it is merged
if (maxNumSegments == 1 && last == 1 && isMerged(infos, infos.info(0), writer)) {
if (verbose(writer)) {
message("already 1 seg; skip", writer);
}
return null;
}
// Check if there are any segments above the threshold
boolean anyTooLarge = false;
for (int i = 0; i < last; i++) {
SegmentCommitInfo info = infos.info(i);
if (size(info, writer) > maxMergeSizeForForcedMerge || sizeDocs(info, writer) > maxMergeDocs) {
anyTooLarge = true;
break;
}
}
if (anyTooLarge) {
return findForcedMergesSizeLimit(infos, maxNumSegments, last, writer);
} else {
return findForcedMergesMaxNumSegments(infos, maxNumSegments, last, writer);
}
}
/**
* Finds merges necessary to force-merge all deletes from the
* index. We simply merge adjacent segments that have
* deletes, up to mergeFactor at a time.
*/
@Override
public MergeSpecification findForcedDeletesMerges(SegmentInfos segmentInfos, IndexWriter writer)
throws IOException {
final List<SegmentCommitInfo> segments = segmentInfos.asList();
final int numSegments = segments.size();
if (verbose(writer)) {
message("findForcedDeleteMerges: " + numSegments + " segments", writer);
}
MergeSpecification spec = new MergeSpecification();
int firstSegmentWithDeletions = -1;
assert writer != null;
for(int i=0;i<numSegments;i++) {
final SegmentCommitInfo info = segmentInfos.info(i);
int delCount = writer.numDeletedDocs(info);
if (delCount > 0) {
if (verbose(writer)) {
message(" segment " + info.info.name + " has deletions", writer);
}
if (firstSegmentWithDeletions == -1)
firstSegmentWithDeletions = i;
else if (i - firstSegmentWithDeletions == mergeFactor) {
// We've seen mergeFactor segments in a row with
// deletions, so force a merge now:
if (verbose(writer)) {
message(" add merge " + firstSegmentWithDeletions + " to " + (i-1) + " inclusive", writer);
}
spec.add(new OneMerge(segments.subList(firstSegmentWithDeletions, i)));
firstSegmentWithDeletions = i;
}
} else if (firstSegmentWithDeletions != -1) {
// End of a sequence of segments with deletions, so,
// merge those past segments even if it's fewer than
// mergeFactor segments
if (verbose(writer)) {
message(" add merge " + firstSegmentWithDeletions + " to " + (i-1) + " inclusive", writer);
}
spec.add(new OneMerge(segments.subList(firstSegmentWithDeletions, i)));
firstSegmentWithDeletions = -1;
}
}
if (firstSegmentWithDeletions != -1) {
if (verbose(writer)) {
message(" add merge " + firstSegmentWithDeletions + " to " + (numSegments-1) + " inclusive", writer);
}
spec.add(new OneMerge(segments.subList(firstSegmentWithDeletions, numSegments)));
}
return spec;
}
private static class SegmentInfoAndLevel implements Comparable<SegmentInfoAndLevel> {
SegmentCommitInfo info;
float level;
public SegmentInfoAndLevel(SegmentCommitInfo info, float level) {
this.info = info;
this.level = level;
}
// Sorts largest to smallest
@Override
public int compareTo(SegmentInfoAndLevel other) {
return Float.compare(other.level, level);
}
}
/** 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. */
@Override
public MergeSpecification findMerges(MergeTrigger mergeTrigger, SegmentInfos infos, IndexWriter writer) throws IOException {
final int numSegments = infos.size();
if (verbose(writer)) {
message("findMerges: " + numSegments + " segments", writer);
}
// Compute levels, which is just log (base mergeFactor)
// of the size of each segment
final List<SegmentInfoAndLevel> levels = new ArrayList<>(numSegments);
final float norm = (float) Math.log(mergeFactor);
final Collection<SegmentCommitInfo> mergingSegments = writer.getMergingSegments();
for(int i=0;i<numSegments;i++) {
final SegmentCommitInfo info = infos.info(i);
long size = size(info, writer);
// Floor tiny segments
if (size < 1) {
size = 1;
}
final SegmentInfoAndLevel infoLevel = new SegmentInfoAndLevel(info, (float) Math.log(size)/norm);
levels.add(infoLevel);
if (verbose(writer)) {
final long segBytes = sizeBytes(info, writer);
String extra = mergingSegments.contains(info) ? " [merging]" : "";
if (size >= maxMergeSize) {
extra += " [skip: too large]";
}
message("seg=" + writer.segString(info) + " level=" + infoLevel.level + " size=" + String.format(Locale.ROOT, "%.3f MB", segBytes/1024/1024.) + extra, writer);
}
}
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;
final int numMergeableSegments = levels.size();
int start = 0;
while(start < numMergeableSegments) {
// Find max level of all segments not already
// quantized.
float maxLevel = levels.get(start).level;
for(int i=1+start;i<numMergeableSegments;i++) {
final float level = levels.get(i).level;
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 = numMergeableSegments-1;
while(upto >= start) {
if (levels.get(upto).level >= levelBottom) {
break;
}
upto--;
}
if (verbose(writer)) {
message(" level " + levelBottom + " to " + maxLevel + ": " + (1+upto-start) + " segments", writer);
}
// Finally, record all merges that are viable at this level:
int end = start + mergeFactor;
while(end <= 1+upto) {
boolean anyTooLarge = false;
boolean anyMerging = false;
for(int i=start;i<end;i++) {
final SegmentCommitInfo info = levels.get(i).info;
anyTooLarge |= (size(info, writer) >= maxMergeSize || sizeDocs(info, writer) >= maxMergeDocs);
if (mergingSegments.contains(info)) {
anyMerging = true;
break;
}
}
if (anyMerging) {
// skip
} else if (!anyTooLarge) {
if (spec == null)
spec = new MergeSpecification();
final List<SegmentCommitInfo> mergeInfos = new ArrayList<>(end-start);
for(int i=start;i<end;i++) {
mergeInfos.add(levels.get(i).info);
assert infos.contains(levels.get(i).info);
}
if (verbose(writer)) {
message(" add merge=" + writer.segString(mergeInfos) + " start=" + start + " end=" + end, writer);
}
spec.add(new OneMerge(mergeInfos));
} else if (verbose(writer)) {
message(" " + start + " to " + end + ": contains segment over maxMergeSize or maxMergeDocs; skipping", writer);
}
start = end;
end = start + mergeFactor;
}
start = 1+upto;
}
return spec;
}
/** <p>Determines the largest segment (measured by
* document count) that may be merged with other segments.
* Small values (e.g., less than 10,000) are best for
* interactive indexing, as this limits the length of
* pauses while indexing to a few seconds. Larger values
* are best for batched indexing and speedier
* searches.</p>
*
* <p>The default value is {@link Integer#MAX_VALUE}.</p>
*
* <p>The default merge policy ({@link
* LogByteSizeMergePolicy}) also allows you to set this
* limit by net size (in MB) of the segment, using {@link
* LogByteSizeMergePolicy#setMaxMergeMB}.</p>
*/
public void setMaxMergeDocs(int maxMergeDocs) {
this.maxMergeDocs = maxMergeDocs;
}
/** Returns the largest segment (measured by document
* count) that may be merged with other segments.
* @see #setMaxMergeDocs */
public int getMaxMergeDocs() {
return maxMergeDocs;
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder("[" + getClass().getSimpleName() + ": ");
sb.append("minMergeSize=").append(minMergeSize).append(", ");
sb.append("mergeFactor=").append(mergeFactor).append(", ");
sb.append("maxMergeSize=").append(maxMergeSize).append(", ");
sb.append("maxMergeSizeForForcedMerge=").append(maxMergeSizeForForcedMerge).append(", ");
sb.append("calibrateSizeByDeletes=").append(calibrateSizeByDeletes).append(", ");
sb.append("maxMergeDocs=").append(maxMergeDocs).append(", ");
sb.append("maxCFSSegmentSizeMB=").append(getMaxCFSSegmentSizeMB()).append(", ");
sb.append("noCFSRatio=").append(noCFSRatio);
sb.append("]");
return sb.toString();
}
}