Class TieredMergePolicy
- java.lang.Object
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- org.apache.lucene.index.MergePolicy
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- org.apache.lucene.index.TieredMergePolicy
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- All Implemented Interfaces:
Closeable
,AutoCloseable
public class TieredMergePolicy extends MergePolicy
Merges segments of approximately equal size, subject to an allowed number of segments per tier. This is similar toLogByteSizeMergePolicy
, except this merge policy is able to merge non-adjacent segment, and separates how many segments are merged at once (setMaxMergeAtOnce(int)
) from how many segments are allowed per tier (setSegmentsPerTier(double)
). This merge policy also does not over-merge (i.e. cascade merges).For normal merging, this policy first computes a "budget" of how many segments are allowed by be in the index. If the index is over-budget, then the policy sorts segments by decreasing size (pro-rating by percent deletes), and then finds the least-cost merge. Merge cost is measured by a combination of the "skew" of the merge (size of largest segment divided by smallest segment), total merge size and percent deletes reclaimed, so that merges with lower skew, smaller size and those reclaiming more deletes, are favored.
If a merge will produce a segment that's larger than
setMaxMergedSegmentMB(double)
, then the policy will merge fewer segments (down to 1 at once, if that one has deletions) to keep the segment size under budget.NOTE: this policy freely merges non-adjacent segments; if this is a problem, use
LogMergePolicy
.NOTE: This policy always merges by byte size of the segments, always pro-rates by percent deletes, and does not apply any maximum segment size during forceMerge (unlike
LogByteSizeMergePolicy
).- 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 protected static class
TieredMergePolicy.MergeScore
Holds score and explanation for a single candidate merge.-
Nested classes/interfaces inherited from class org.apache.lucene.index.MergePolicy
MergePolicy.MergeAbortedException, MergePolicy.MergeException, MergePolicy.MergeSpecification, MergePolicy.OneMerge
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Field Summary
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Fields inherited from class org.apache.lucene.index.MergePolicy
writer
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Constructor Summary
Constructors Constructor Description TieredMergePolicy()
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
close()
Release all resources for the policy.MergePolicy.MergeSpecification
findForcedDeletesMerges(SegmentInfos infos)
Determine what set of merge operations is necessary in order to expunge all deletes from the index.MergePolicy.MergeSpecification
findForcedMerges(SegmentInfos infos, int maxSegmentCount, Map<SegmentInfo,Boolean> segmentsToMerge)
Determine what set of merge operations is necessary in order to merge to <= the specified segment count.MergePolicy.MergeSpecification
findMerges(SegmentInfos infos)
Determine what set of merge operations are now necessary on the index.double
getFloorSegmentMB()
double
getForceMergeDeletesPctAllowed()
int
getMaxMergeAtOnce()
int
getMaxMergeAtOnceExplicit()
double
getMaxMergedSegmentMB()
double
getNoCFSRatio()
double
getReclaimDeletesWeight()
double
getSegmentsPerTier()
boolean
getUseCompoundFile()
protected TieredMergePolicy.MergeScore
score(List<SegmentInfo> candidate, boolean hitTooLarge, long mergingBytes)
Expert: scores one merge; subclasses can override.TieredMergePolicy
setFloorSegmentMB(double v)
Segments smaller than this are "rounded up" to this size, ie treated as equal (floor) size for merge selection.TieredMergePolicy
setForceMergeDeletesPctAllowed(double v)
When forceMergeDeletes is called, we only merge away a segment if its delete percentage is over this threshold.TieredMergePolicy
setMaxMergeAtOnce(int v)
Maximum number of segments to be merged at a time during "normal" merging.TieredMergePolicy
setMaxMergeAtOnceExplicit(int v)
Maximum number of segments to be merged at a time, during forceMerge or forceMergeDeletes.TieredMergePolicy
setMaxMergedSegmentMB(double v)
Maximum sized segment to produce during normal merging.TieredMergePolicy
setNoCFSRatio(double 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.TieredMergePolicy
setReclaimDeletesWeight(double v)
Controls how aggressively merges that reclaim more deletions are favored.TieredMergePolicy
setSegmentsPerTier(double v)
Sets the allowed number of segments per tier.TieredMergePolicy
setUseCompoundFile(boolean useCompoundFile)
Sets whether compound file format should be used for newly flushed and newly merged segments.String
toString()
boolean
useCompoundFile(SegmentInfos infos, SegmentInfo mergedInfo)
Returns true if a new segment (regardless of its origin) should use the compound file format.-
Methods inherited from class org.apache.lucene.index.MergePolicy
setIndexWriter
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Method Detail
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setMaxMergeAtOnce
public TieredMergePolicy setMaxMergeAtOnce(int v)
Maximum number of segments to be merged at a time during "normal" merging. For explicit merging (eg, forceMerge or forceMergeDeletes was called), seesetMaxMergeAtOnceExplicit(int)
. Default is 10.
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getMaxMergeAtOnce
public int getMaxMergeAtOnce()
- See Also:
setMaxMergeAtOnce(int)
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setMaxMergeAtOnceExplicit
public TieredMergePolicy setMaxMergeAtOnceExplicit(int v)
Maximum number of segments to be merged at a time, during forceMerge or forceMergeDeletes. Default is 30.
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getMaxMergeAtOnceExplicit
public int getMaxMergeAtOnceExplicit()
- See Also:
setMaxMergeAtOnceExplicit(int)
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setMaxMergedSegmentMB
public TieredMergePolicy setMaxMergedSegmentMB(double v)
Maximum sized segment to produce during normal merging. This setting is approximate: the estimate of the merged segment size is made by summing sizes of to-be-merged segments (compensating for percent deleted docs). Default is 5 GB.
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getMaxMergedSegmentMB
public double getMaxMergedSegmentMB()
- See Also:
getMaxMergedSegmentMB()
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setReclaimDeletesWeight
public TieredMergePolicy setReclaimDeletesWeight(double v)
Controls how aggressively merges that reclaim more deletions are favored. Higher values favor selecting merges that reclaim deletions. A value of 0.0 means deletions don't impact merge selection.
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getReclaimDeletesWeight
public double getReclaimDeletesWeight()
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setFloorSegmentMB
public TieredMergePolicy setFloorSegmentMB(double v)
Segments smaller than this are "rounded up" to this size, ie treated as equal (floor) size for merge selection. This is to prevent frequent flushing of tiny segments from allowing a long tail in the index. Default is 2 MB.
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getFloorSegmentMB
public double getFloorSegmentMB()
- See Also:
setFloorSegmentMB(double)
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setForceMergeDeletesPctAllowed
public TieredMergePolicy setForceMergeDeletesPctAllowed(double v)
When forceMergeDeletes is called, we only merge away a segment if its delete percentage is over this threshold. Default is 10%.
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getForceMergeDeletesPctAllowed
public double getForceMergeDeletesPctAllowed()
- See Also:
setForceMergeDeletesPctAllowed(double)
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setSegmentsPerTier
public TieredMergePolicy setSegmentsPerTier(double v)
Sets the allowed number of segments per tier. Smaller values mean more merging but fewer segments.NOTE: this value should be >= the
setMaxMergeAtOnce(int)
otherwise you'll force too much merging to occur.Default is 10.0.
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getSegmentsPerTier
public double getSegmentsPerTier()
- See Also:
setSegmentsPerTier(double)
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setUseCompoundFile
public TieredMergePolicy setUseCompoundFile(boolean useCompoundFile)
Sets whether compound file format should be used for newly flushed and newly merged segments. Default true.
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getUseCompoundFile
public boolean getUseCompoundFile()
- See Also:
setUseCompoundFile(boolean)
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setNoCFSRatio
public TieredMergePolicy setNoCFSRatio(double 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. Default is 0.1.
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getNoCFSRatio
public double getNoCFSRatio()
- See Also:
setNoCFSRatio(double)
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findMerges
public MergePolicy.MergeSpecification findMerges(SegmentInfos infos) throws IOException
Description copied from class:MergePolicy
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.- Specified by:
findMerges
in classMergePolicy
- Parameters:
infos
- the total set of segments in the index- Throws:
IOException
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score
protected TieredMergePolicy.MergeScore score(List<SegmentInfo> candidate, boolean hitTooLarge, long mergingBytes) throws IOException
Expert: scores one merge; subclasses can override.- Throws:
IOException
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findForcedMerges
public MergePolicy.MergeSpecification findForcedMerges(SegmentInfos infos, int maxSegmentCount, Map<SegmentInfo,Boolean> segmentsToMerge) throws IOException
Description copied from class:MergePolicy
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.- Specified by:
findForcedMerges
in classMergePolicy
- Parameters:
infos
- 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:
IOException
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findForcedDeletesMerges
public MergePolicy.MergeSpecification findForcedDeletesMerges(SegmentInfos infos) throws CorruptIndexException, IOException
Description copied from class:MergePolicy
Determine what set of merge operations is necessary in order to expunge all deletes from the index.- Specified by:
findForcedDeletesMerges
in classMergePolicy
- Parameters:
infos
- the total set of segments in the index- Throws:
CorruptIndexException
IOException
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useCompoundFile
public boolean useCompoundFile(SegmentInfos infos, SegmentInfo mergedInfo) throws IOException
Description copied from class:MergePolicy
Returns true if a new segment (regardless of its origin) should use the compound file format.- Specified by:
useCompoundFile
in classMergePolicy
- Throws:
IOException
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close
public void close()
Description copied from class:MergePolicy
Release all resources for the policy.- Specified by:
close
in interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Specified by:
close
in classMergePolicy
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