Class MergePolicy

Expert: a MergePolicy determines the sequence of primitive merge operations.

Whenever the segments in an index have been altered by 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, IndexWriter invokes FindMerges(MergeTrigger, SegmentInfos) to give the MergePolicy a chance to pick merges that are now required. This method returns a MergePolicy.MergeSpecification instance describing the set of merges that should be done, or null if no merges are necessary. When ForceMerge(Int32) is called, it calls FindForcedMerges(SegmentInfos, Int32, IDictionary<SegmentCommitInfo, Nullable<Boolean>>) and the MergePolicy should then return the necessary merges.

Note that the policy can return more than one merge at a time. In this case, if the writer is using SerialMergeScheduler, the merges will be run sequentially but if it is using ConcurrentMergeScheduler they will be run concurrently.

The default MergePolicy is TieredMergePolicy.

This is a Lucene.NET EXPERIMENTAL API, use at your own risk

Inheritance

System.Object

MergePolicy

LogMergePolicy

NoMergePolicy

TieredMergePolicy

UpgradeIndexMergePolicy

Namespace: Lucene.Net.Index

Assembly: Lucene.Net.dll

Syntax

public abstract class MergePolicy : IDisposable

Constructors

MergePolicy()

Creates a new merge policy instance. Note that if you intend to use it without passing it to IndexWriter, you should call SetIndexWriter(IndexWriter).

Declaration

public MergePolicy()

MergePolicy(Double, Int64)

Creates a new merge policy instance with default settings for m_noCFSRatio and m_maxCFSSegmentSize. This ctor should be used by subclasses using different defaults than the MergePolicy

Declaration

protected MergePolicy(double defaultNoCFSRatio, long defaultMaxCFSSegmentSize)

Parameters

Type	Name	Description
System.Double	defaultNoCFSRatio
System.Int64	defaultMaxCFSSegmentSize

Fields

DEFAULT_MAX_CFS_SEGMENT_SIZE

Default max segment size in order to use compound file system. Set to .

Declaration

protected static readonly long DEFAULT_MAX_CFS_SEGMENT_SIZE

Field Value

Type	Description
System.Int64

DEFAULT_NO_CFS_RATIO

Default ratio for compound file system usage. Set to 1.0, always use compound file system.

Declaration

protected static readonly double DEFAULT_NO_CFS_RATIO

Field Value

Type	Description
System.Double

m_maxCFSSegmentSize

If the size of the merged segment exceeds this value then it will not use compound file format.

Declaration

protected long m_maxCFSSegmentSize

Field Value

Type	Description
System.Int64

m_noCFSRatio

If the size of the merge segment exceeds this ratio of the total index size then it will remain in non-compound format

Declaration

protected double m_noCFSRatio

Field Value

Type	Description
System.Double

m_writer

IndexWriter that contains this instance.

Declaration

protected SetOnce<IndexWriter> m_writer

Field Value

Type	Description
SetOnce<IndexWriter>

Properties

MaxCFSSegmentSizeMB

Gets or Sets the largest size allowed for a compound file segment.

If a merged segment will be more than this value, leave the segment as non-compound file even if compound file is enabled. Set this to (default) and NoCFSRatio to 1.0 to always use CFS regardless of merge size.

Declaration

public double MaxCFSSegmentSizeMB { get; set; }

Property Value

Type	Description
System.Double

NoCFSRatio

Gets or Sets current m_noCFSRatio.

If a merged segment will be more than this percentage of the total size of the index, leave the segment as non-compound file even if compound file is enabled. Set to 1.0 to always use CFS regardless of merge size.

Declaration

public double NoCFSRatio { get; set; }

Property Value

Type	Description
System.Double

Methods

Clone()

Declaration

public virtual object Clone()

Returns

Type	Description
System.Object

Dispose()

Release all resources for the policy.

Declaration

public void Dispose()

Dispose(Boolean)

Release all resources for the policy.

Declaration

protected abstract void Dispose(bool disposing)

Parameters

Type	Name	Description
System.Boolean	disposing

FindForcedDeletesMerges(SegmentInfos)

Determine what set of merge operations is necessary in order to expunge all deletes from the index.

Declaration

public abstract MergePolicy.MergeSpecification FindForcedDeletesMerges(SegmentInfos segmentInfos)

Parameters

Type	Name	Description
SegmentInfos	segmentInfos	the total set of segments in the index

Returns

Type	Description
MergePolicy.MergeSpecification

FindForcedMerges(SegmentInfos, Int32, IDictionary<SegmentCommitInfo, Nullable<Boolean>>)

Determine what set of merge operations is necessary in order to merge to <= the specified segment count. IndexWriter calls this when its ForceMerge(Int32, Boolean) method is called. This call is always synchronized on the IndexWriter instance so only one thread at a time will call this method.

Declaration

public abstract MergePolicy.MergeSpecification FindForcedMerges(SegmentInfos segmentInfos, int maxSegmentCount, IDictionary<SegmentCommitInfo, bool?> segmentsToMerge)

Parameters

Type	Name	Description
SegmentInfos	segmentInfos	The total set of segments in the index
System.Int32	maxSegmentCount	Requested maximum number of segments in the index (currently this is always 1)
IDictionary<SegmentCommitInfo, System.Nullable<System.Boolean>>	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.

Returns

Type	Description
MergePolicy.MergeSpecification

FindMerges(MergeTrigger, SegmentInfos)

Determine what set of merge operations are now necessary on the index. IndexWriter calls this whenever there is a change to the segments. This call is always synchronized on the IndexWriter instance so only one thread at a time will call this method.

Declaration

public abstract MergePolicy.MergeSpecification FindMerges(MergeTrigger mergeTrigger, SegmentInfos segmentInfos)

Parameters

Type	Name	Description
MergeTrigger	mergeTrigger	the event that triggered the merge
SegmentInfos	segmentInfos	the total set of segments in the index

Returns

Type	Description
MergePolicy.MergeSpecification

IsMerged(SegmentInfos, SegmentCommitInfo)

Returns true if this single info is already fully merged (has no pending deletes, is in the same dir as the writer, and matches the current compound file setting

Declaration

protected bool IsMerged(SegmentInfos infos, SegmentCommitInfo info)

Parameters

Type	Name	Description
SegmentInfos	infos
SegmentCommitInfo	info

Returns

Type	Description
System.Boolean

SetIndexWriter(IndexWriter)

Sets the 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, AlreadySetException is thrown.

Declaration

public virtual void SetIndexWriter(IndexWriter writer)

Parameters

Type	Name	Description
IndexWriter	writer

See Also

SetOnce<T>

Size(SegmentCommitInfo)

Return the byte size of the provided SegmentCommitInfo, pro-rated by percentage of non-deleted documents is set.

Declaration

protected virtual long Size(SegmentCommitInfo info)

Parameters

Type	Name	Description
SegmentCommitInfo	info

Returns

Type	Description
System.Int64

UseCompoundFile(SegmentInfos, SegmentCommitInfo)

Returns true if a new segment (regardless of its origin) should use the compound file format. The default implementation returns true iff the size of the given mergedInfo is less or equal to MaxCFSSegmentSizeMB and the size is less or equal to the TotalIndexSize * NoCFSRatio otherwise

false

.

Declaration

public virtual bool UseCompoundFile(SegmentInfos infos, SegmentCommitInfo mergedInfo)

Parameters

Type	Name	Description
SegmentInfos	infos
SegmentCommitInfo	mergedInfo

Returns

Type	Description
System.Boolean