public abstract class

MergePolicy

extends Object
implements Closeable
java.lang.Object
   ↳ org.apache.lucene.index.MergePolicy
Known Direct Subclasses
Known Indirect Subclasses

Class Overview

Expert: a MergePolicy determines the sequence of primitive merge operations to be used for overall merge and optimize 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(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 IndexWriter.optimize is called, it calls findMergesForOptimize(SegmentInfos, int, Set) 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 LogByteSizeMergePolicy.

NOTE: This API is new and still experimental (subject to change suddenly in the next release)

NOTE: This class typically requires access to package-private APIs (e.g. SegmentInfos) to do its job; if you implement your own MergePolicy, you'll need to put it in package org.apache.lucene.index in order to use these APIs.

Summary

Nested Classes
class MergePolicy.MergeAbortedException  
class MergePolicy.MergeException Exception thrown if there are any problems while executing a merge. 
class MergePolicy.MergeSpecification A MergeSpecification instance provides the information necessary to perform multiple merges. 
class MergePolicy.OneMerge OneMerge provides the information necessary to perform an individual primitive merge operation, resulting in a single new segment. 
Fields
protected final IndexWriter writer
Public Constructors
MergePolicy(IndexWriter writer)
Public Methods
abstract void close()
Release all resources for the policy.
abstract MergePolicy.MergeSpecification findMerges(SegmentInfos segmentInfos)
Determine what set of merge operations are now necessary on the index.
abstract MergePolicy.MergeSpecification findMergesForOptimize(SegmentInfos segmentInfos, int maxSegmentCount, Set<SegmentInfo> segmentsToOptimize)
Determine what set of merge operations is necessary in order to optimize the index.
abstract MergePolicy.MergeSpecification findMergesToExpungeDeletes(SegmentInfos segmentInfos)
Determine what set of merge operations is necessary in order to expunge all deletes from the index.
abstract boolean useCompoundDocStore(SegmentInfos segments)
Returns true if the doc store files should use the compound file format.
abstract boolean useCompoundFile(SegmentInfos segments, SegmentInfo newSegment)
Returns true if a newly flushed (not from merge) segment should use the compound file format.
[Expand]
Inherited Methods
From class java.lang.Object
From interface java.io.Closeable

Fields

protected final IndexWriter writer

Public Constructors

public MergePolicy (IndexWriter writer)

Public Methods

public abstract void close ()

Release all resources for the policy.

public abstract MergePolicy.MergeSpecification findMerges (SegmentInfos 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.

Parameters
segmentInfos the total set of segments in the index
Throws
CorruptIndexException
IOException

public abstract MergePolicy.MergeSpecification findMergesForOptimize (SegmentInfos segmentInfos, int maxSegmentCount, Set<SegmentInfo> segmentsToOptimize)

Determine what set of merge operations is necessary in order to optimize the index. IndexWriter calls this when its optimize() method is called. This call is always synchronized on the IndexWriter instance so only one thread at a time will call this method.

Parameters
segmentInfos the total set of segments in the index
maxSegmentCount requested maximum number of segments in the index (currently this is always 1)
segmentsToOptimize contains the specific SegmentInfo instances that must be merged away. This may be a subset of all SegmentInfos.
Throws
CorruptIndexException
IOException

public abstract MergePolicy.MergeSpecification findMergesToExpungeDeletes (SegmentInfos segmentInfos)

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

Parameters
segmentInfos the total set of segments in the index
Throws
CorruptIndexException
IOException

public abstract boolean useCompoundDocStore (SegmentInfos segments)

Returns true if the doc store files should use the compound file format.

public abstract boolean useCompoundFile (SegmentInfos segments, SegmentInfo newSegment)

Returns true if a newly flushed (not from merge) segment should use the compound file format.