org.apache.lucene.index

Class LogMergePolicy

java.lang.Object

org.apache.lucene.index.MergePolicy

org.apache.lucene.index.LogMergePolicy

Direct Known Subclasses:

LogByteSizeMergePolicy, LogDocMergePolicy

public abstract class LogMergePolicy
extends MergePolicy

This class implements a 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 getMergeFactor() and setMergeFactor(int) respectively.

This class is abstract and requires a subclass to define the MergePolicy.size(org.apache.lucene.index.SegmentCommitInfo, org.apache.lucene.index.MergePolicy.MergeContext) method which specifies how a segment's size is determined. LogDocMergePolicy is one subclass that measures size by document count in the segment. LogByteSizeMergePolicy is another subclass that measures size as the total byte size of the file(s) for the segment.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.index.MergePolicy

MergePolicy.MergeAbortedException, MergePolicy.MergeContext, MergePolicy.MergeException, MergePolicy.MergeSpecification, MergePolicy.OneMerge, MergePolicy.OneMergeProgress

Field Summary

Fields

Modifier and Type	Field and Description
protected boolean	calibrateSizeByDeletes If true, we pro-rate a segment's size by the percentage of non-deleted documents.
static int	DEFAULT_MAX_MERGE_DOCS Default maximum segment size.
static int	DEFAULT_MERGE_FACTOR Default merge factor, which is how many segments are merged at a time
static double	DEFAULT_NO_CFS_RATIO Default noCFSRatio.
static double	LEVEL_LOG_SPAN Defines the allowed range of log(size) for each level.
protected int	maxMergeDocs If a segment has more than this many documents then it will never be merged.
protected long	maxMergeSize If the size of a segment exceeds this value then it will never be merged.
protected long	maxMergeSizeForForcedMerge If the size of a segment exceeds this value then it will never be merged during IndexWriter.forceMerge(int).
protected int	mergeFactor How many segments to merge at a time.
protected long	minMergeSize Any segments whose size is smaller than this value will be rounded up to this value.

Fields inherited from class org.apache.lucene.index.MergePolicy

DEFAULT_MAX_CFS_SEGMENT_SIZE, maxCFSSegmentSize, noCFSRatio

Constructor Summary

Constructors

Constructor and Description
LogMergePolicy() Sole constructor.

Method Summary

Modifier and Type	Method and Description
MergePolicy.MergeSpecification	findForcedDeletesMerges(SegmentInfos segmentInfos, MergePolicy.MergeContext mergeContext) Finds merges necessary to force-merge all deletes from the index.
MergePolicy.MergeSpecification	findForcedMerges(SegmentInfos infos, int maxNumSegments, Map<SegmentCommitInfo,Boolean> segmentsToMerge, MergePolicy.MergeContext mergeContext) Returns the merges necessary to merge the index down to a specified number of segments.
MergePolicy.MergeSpecification	findMerges(MergeTrigger mergeTrigger, SegmentInfos infos, MergePolicy.MergeContext mergeContext) Checks if any merges are now necessary and returns a MergePolicy.MergeSpecification if so.
boolean	getCalibrateSizeByDeletes() Returns true if the segment size should be calibrated by the number of deletes when choosing segments for merge.
int	getMaxMergeDocs() Returns the largest segment (measured by document count) that may be merged with other segments.
int	getMergeFactor() Returns the number of segments that are merged at once and also controls the total number of segments allowed to accumulate in the index.
protected boolean	isMerged(SegmentInfos infos, int maxNumSegments, Map<SegmentCommitInfo,Boolean> segmentsToMerge, MergePolicy.MergeContext mergeContext) Returns true if the number of segments eligible for merging is less than or equal to the specified maxNumSegments.
void	setCalibrateSizeByDeletes(boolean calibrateSizeByDeletes) Sets whether the segment size should be calibrated by the number of deletes when choosing segments for merge.
void	setMaxMergeDocs(int maxMergeDocs) Determines the largest segment (measured by document count) that may be merged with other segments.
void	setMergeFactor(int mergeFactor) Determines how often segment indices are merged by addDocument().
protected long	sizeBytes(SegmentCommitInfo info, MergePolicy.MergeContext mergeContext) Return the byte size of the provided SegmentCommitInfo, pro-rated by percentage of non-deleted documents if setCalibrateSizeByDeletes(boolean) is set.
protected long	sizeDocs(SegmentCommitInfo info, MergePolicy.MergeContext mergeContext) Return the number of documents in the provided SegmentCommitInfo, pro-rated by percentage of non-deleted documents if setCalibrateSizeByDeletes(boolean) is set.
String	toString()

Methods inherited from class org.apache.lucene.index.MergePolicy

assertDelCount, findFullFlushMerges, getMaxCFSSegmentSizeMB, getNoCFSRatio, isMerged, keepFullyDeletedSegment, message, numDeletesToMerge, segString, setMaxCFSSegmentSizeMB, setNoCFSRatio, size, useCompoundFile, verbose

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

LEVEL_LOG_SPAN

public static final double LEVEL_LOG_SPAN

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.

See Also:

Constant Field Values

DEFAULT_MERGE_FACTOR

public static final int DEFAULT_MERGE_FACTOR

Default merge factor, which is how many segments are merged at a time

See Also:

Constant Field Values

DEFAULT_MAX_MERGE_DOCS

public static final int DEFAULT_MAX_MERGE_DOCS

Default maximum segment size. A segment of this size or larger will never be merged. @see setMaxMergeDocs

See Also:

Constant Field Values

DEFAULT_NO_CFS_RATIO

public static final double DEFAULT_NO_CFS_RATIO

Default noCFSRatio. If a merge's size is >= 10% of the index, then we disable compound file for it.

See Also:

MergePolicy.setNoCFSRatio(double), Constant Field Values

mergeFactor

protected int mergeFactor

How many segments to merge at a time.

minMergeSize

protected long minMergeSize

Any segments whose size is smaller than this value will be rounded up to this value. This ensures that tiny segments are aggressively merged.

maxMergeSize

protected long maxMergeSize

If the size of a segment exceeds this value then it will never be merged.

maxMergeSizeForForcedMerge

protected long maxMergeSizeForForcedMerge

If the size of a segment exceeds this value then it will never be merged during IndexWriter.forceMerge(int).

maxMergeDocs

protected int maxMergeDocs

If a segment has more than this many documents then it will never be merged.

calibrateSizeByDeletes

protected boolean calibrateSizeByDeletes

If true, we pro-rate a segment's size by the percentage of non-deleted documents.

Constructor Detail

LogMergePolicy

public LogMergePolicy()

Sole constructor. (For invocation by subclass constructors, typically implicit.)

Method Detail

getMergeFactor

public int getMergeFactor()

Returns the number of segments that are merged at once and also controls the total number of segments allowed to accumulate in the index.

setMergeFactor

public void setMergeFactor(int 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 (> 10) are best for batch index creation, and smaller values (< 10) for indices that are interactively maintained.

setCalibrateSizeByDeletes

public void setCalibrateSizeByDeletes(boolean calibrateSizeByDeletes)

Sets whether the segment size should be calibrated by the number of deletes when choosing segments for merge.

getCalibrateSizeByDeletes

public boolean getCalibrateSizeByDeletes()

Returns true if the segment size should be calibrated by the number of deletes when choosing segments for merge.

sizeDocs

protected long sizeDocs(SegmentCommitInfo info,
                        MergePolicy.MergeContext mergeContext)
                 throws IOException

Return the number of documents in the provided SegmentCommitInfo, pro-rated by percentage of non-deleted documents if setCalibrateSizeByDeletes(boolean) is set.

Throws:

IOException

sizeBytes

protected long sizeBytes(SegmentCommitInfo info,
                         MergePolicy.MergeContext mergeContext)
                  throws IOException

Return the byte size of the provided SegmentCommitInfo, pro-rated by percentage of non-deleted documents if setCalibrateSizeByDeletes(boolean) is set.

Throws:

IOException

isMerged

protected boolean isMerged(SegmentInfos infos,
                           int maxNumSegments,
                           Map<SegmentCommitInfo,Boolean> segmentsToMerge,
                           MergePolicy.MergeContext mergeContext)
                    throws IOException

Returns true if the number of segments eligible for merging is less than or equal to the specified maxNumSegments.

Throws:

IOException

findForcedMerges

public MergePolicy.MergeSpecification findForcedMerges(SegmentInfos infos,
                                                       int maxNumSegments,
                                                       Map<SegmentCommitInfo,Boolean> segmentsToMerge,
                                                       MergePolicy.MergeContext mergeContext)
                                                throws IOException

Returns the merges necessary to merge the index down to a specified number of segments. This respects the maxMergeSizeForForcedMerge setting. By default, and assuming 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 MergeScheduler in use may make use of concurrency.

Specified by:

findForcedMerges in class MergePolicy

Parameters:

infos - the total set of segments in the index

maxNumSegments - requested maximum number of segments in the index (currently this is always 1)

segmentsToMerge - 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-merged index; else, it was a segment produced by a cascaded merge.

mergeContext - the MergeContext to find the merges on

Throws:

IOException

findForcedDeletesMerges

public MergePolicy.MergeSpecification findForcedDeletesMerges(SegmentInfos segmentInfos,
                                                              MergePolicy.MergeContext mergeContext)
                                                       throws IOException

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.

Specified by:

findForcedDeletesMerges in class MergePolicy

Parameters:

segmentInfos - the total set of segments in the index

mergeContext - the MergeContext to find the merges on

Throws:

IOException

findMerges

public MergePolicy.MergeSpecification findMerges(MergeTrigger mergeTrigger,
                                                 SegmentInfos infos,
                                                 MergePolicy.MergeContext mergeContext)
                                          throws IOException

Checks if any merges are now necessary and returns a MergePolicy.MergeSpecification if so. A merge is necessary when there are more than setMergeFactor(int) segments at a given level. When multiple levels have too many segments, this method will return multiple merges, allowing the MergeScheduler to use concurrency.

Specified by:

findMerges in class MergePolicy

Parameters:

mergeTrigger - the event that triggered the merge

infos - the total set of segments in the index

mergeContext - the IndexWriter to find the merges on

Throws:

IOException

setMaxMergeDocs

public void setMaxMergeDocs(int maxMergeDocs)

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.

The default value is Integer.MAX_VALUE.

The default merge policy (LogByteSizeMergePolicy) also allows you to set this limit by net size (in MB) of the segment, using LogByteSizeMergePolicy.setMaxMergeMB(double).

getMaxMergeDocs

public int getMaxMergeDocs()

Returns the largest segment (measured by document count) that may be merged with other segments.

See Also:

setMaxMergeDocs(int)

toString

public String toString()

Overrides:

toString in class Object