org.apache.lucene.index
Class MergePolicy

java.lang.Object
  extended by org.apache.lucene.index.MergePolicy
All Implemented Interfaces:
Closeable
Direct Known Subclasses:
LogMergePolicy

public abstract class MergePolicy
extends Object
implements Closeable

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(org.apache.lucene.index.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(org.apache.lucene.index.SegmentInfos, int, java.util.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.


Nested Class Summary
static class MergePolicy.MergeAbortedException
           
static class MergePolicy.MergeException
          Exception thrown if there are any problems while executing a merge.
static class MergePolicy.MergeSpecification
          A MergeSpecification instance provides the information necessary to perform multiple merges.
static class MergePolicy.OneMerge
          OneMerge provides the information necessary to perform an individual primitive merge operation, resulting in a single new segment.
 
Field Summary
protected  IndexWriter writer
           
 
Constructor Summary
MergePolicy(IndexWriter writer)
           
 
Method Summary
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.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

writer

protected final IndexWriter writer
Constructor Detail

MergePolicy

public MergePolicy(IndexWriter writer)
Method Detail

findMerges

public abstract MergePolicy.MergeSpecification findMerges(SegmentInfos segmentInfos)
                                                   throws CorruptIndexException,
                                                          IOException
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

findMergesForOptimize

public abstract MergePolicy.MergeSpecification findMergesForOptimize(SegmentInfos segmentInfos,
                                                                     int maxSegmentCount,
                                                                     Set<SegmentInfo> segmentsToOptimize)
                                                              throws CorruptIndexException,
                                                                     IOException
Determine what set of merge operations is necessary in order to optimize the index. IndexWriter calls this when its IndexWriter.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

findMergesToExpungeDeletes

public abstract MergePolicy.MergeSpecification findMergesToExpungeDeletes(SegmentInfos segmentInfos)
                                                                   throws CorruptIndexException,
                                                                          IOException
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

close

public abstract void close()
Release all resources for the policy.

Specified by:
close in interface Closeable

useCompoundFile

public abstract boolean useCompoundFile(SegmentInfos segments,
                                        SegmentInfo newSegment)
Returns true if a newly flushed (not from merge) segment should use the compound file format.


useCompoundDocStore

public abstract boolean useCompoundDocStore(SegmentInfos segments)
Returns true if the doc store files should use the compound file format.



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