Class MergePolicy
- java.lang.Object
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- org.apache.lucene.index.MergePolicy
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- All Implemented Interfaces:
Closeable
,AutoCloseable
- Direct Known Subclasses:
LogMergePolicy
,NoMergePolicy
,TieredMergePolicy
,UpgradeIndexMergePolicy
public abstract class MergePolicy extends Object implements Closeable
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
invokesfindMerges(org.apache.lucene.index.SegmentInfos)
to give the MergePolicy a chance to pick merges that are now required. This method returns aMergePolicy.MergeSpecification
instance describing the set of merges that should be done, or null if no merges are necessary. When IndexWriter.forceMerge is called, it callsfindForcedMerges(SegmentInfos,int,Map)
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 usingConcurrentMergeScheduler
they will be run concurrently.The default MergePolicy is
TieredMergePolicy
.- WARNING: This API is experimental and might change in incompatible ways in the next release.
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Nested Class Summary
Nested Classes Modifier and Type Class Description 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.
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Field Summary
Fields Modifier and Type Field Description protected SetOnce<IndexWriter>
writer
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Constructor Summary
Constructors Constructor Description MergePolicy()
Creates a new merge policy instance.
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description abstract void
close()
Release all resources for the policy.abstract MergePolicy.MergeSpecification
findForcedDeletesMerges(SegmentInfos segmentInfos)
Determine what set of merge operations is necessary in order to expunge all deletes from the index.abstract MergePolicy.MergeSpecification
findForcedMerges(SegmentInfos segmentInfos, int maxSegmentCount, Map<SegmentInfo,Boolean> segmentsToMerge)
Determine what set of merge operations is necessary in order to merge to <= the specified segment count.abstract MergePolicy.MergeSpecification
findMerges(SegmentInfos segmentInfos)
Determine what set of merge operations are now necessary on the index.void
setIndexWriter(IndexWriter writer)
Sets theIndexWriter
to use by this merge policy.abstract boolean
useCompoundFile(SegmentInfos segments, SegmentInfo newSegment)
Returns true if a new segment (regardless of its origin) should use the compound file format.
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Field Detail
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writer
protected final SetOnce<IndexWriter> writer
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Constructor Detail
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MergePolicy
public MergePolicy()
Creates a new merge policy instance. Note that if you intend to use it without passing it toIndexWriter
, you should callsetIndexWriter(IndexWriter)
.
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Method Detail
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setIndexWriter
public void setIndexWriter(IndexWriter writer)
Sets theIndexWriter
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,SetOnce.AlreadySetException
is thrown.- See Also:
SetOnce
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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 theIndexWriter
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
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findForcedMerges
public abstract MergePolicy.MergeSpecification findForcedMerges(SegmentInfos segmentInfos, int maxSegmentCount, Map<SegmentInfo,Boolean> segmentsToMerge) throws CorruptIndexException, IOException
Determine what set of merge operations is necessary in order to merge to <= the specified segment count.IndexWriter
calls this when itsIndexWriter.forceMerge(int)
method is called. This call is always synchronized on theIndexWriter
instance so only one thread at a time will call this method.- Parameters:
segmentInfos
- the total set of segments in the indexmaxSegmentCount
- 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.- Throws:
CorruptIndexException
IOException
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findForcedDeletesMerges
public abstract MergePolicy.MergeSpecification findForcedDeletesMerges(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
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close
public abstract void close()
Release all resources for the policy.- Specified by:
close
in interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
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useCompoundFile
public abstract boolean useCompoundFile(SegmentInfos segments, SegmentInfo newSegment) throws IOException
Returns true if a new segment (regardless of its origin) should use the compound file format.- Throws:
IOException
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