Package org.apache.lucene.index

Class MergePolicy

java.lang.Object
org.apache.lucene.index.MergePolicy
All Implemented Interfaces:
Closeable, AutoCloseable, Cloneable
Direct Known Subclasses:
LogMergePolicy, NoMergePolicy, TieredMergePolicy, UpgradeIndexMergePolicy
public abstract class MergePolicy extends Object implements Closeable, Cloneable

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(org.apache.lucene.index.MergePolicy.MergeTrigger, 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.forceMerge is called, it calls findForcedMerges(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 using ConcurrentMergeScheduler they will be run concurrently.

The default MergePolicy is TieredMergePolicy.

  • Field Details

    • DEFAULT_NO_CFS_RATIO

      protected static final double DEFAULT_NO_CFS_RATIO
      Default ratio for compound file system usage. Set to 1.0, always use compound file system.
      See Also:

    • DEFAULT_MAX_CFS_SEGMENT_SIZE

      protected static final long DEFAULT_MAX_CFS_SEGMENT_SIZE
      Default max segment size in order to use compound file system. Set to Long.MAX_VALUE.
      See Also:

    • writer

      protected SetOnce<IndexWriter> writer
      IndexWriter that contains this instance.

    • noCFSRatio

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

    • maxCFSSegmentSize

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

  • Constructor Details

    • MergePolicy

      public 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).

    • MergePolicy

      protected MergePolicy(double defaultNoCFSRatio, long defaultMaxCFSSegmentSize)
      Creates a new merge policy instance with default settings for noCFSRatio and maxCFSSegmentSize. This ctor should be used by subclasses using different defaults than the MergePolicy

  • Method Details

    • clone

      public MergePolicy clone()
      Overrides:
      clone in class Object

    • setIndexWriter

      public void setIndexWriter(IndexWriter writer)
      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, SetOnce.AlreadySetException is thrown.
      See Also:

    • findMerges

      public abstract MergePolicy.MergeSpecification findMerges(MergePolicy.MergeTrigger mergeTrigger, SegmentInfos segmentInfos) throws 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:
      mergeTrigger - the event that triggered the merge
      segmentInfos - the total set of segments in the index
      Throws:
      IOException

    • findForcedMerges

      public abstract MergePolicy.MergeSpecification findForcedMerges(SegmentInfos segmentInfos, int maxSegmentCount, Map<SegmentCommitInfo,Boolean> segmentsToMerge) throws IOException
      Determine what set of merge operations is necessary in order to merge to <= the specified segment count. IndexWriter calls this when its IndexWriter.forceMerge(int) 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)
      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

    • findForcedDeletesMerges

      public abstract MergePolicy.MergeSpecification findForcedDeletesMerges(SegmentInfos segmentInfos) throws 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:
      IOException

    • close

      public abstract void close()
      Release all resources for the policy.
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable

    • useCompoundFile

      public boolean useCompoundFile(SegmentInfos infos, SegmentCommitInfo mergedInfo) throws IOException
      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 getMaxCFSSegmentSizeMB() and the size is less or equal to the TotalIndexSize * getNoCFSRatio() otherwise false.
      Throws:
      IOException

    • size

      protected long size(SegmentCommitInfo info) throws IOException
      Return the byte size of the provided SegmentCommitInfo, pro-rated by percentage of non-deleted documents is set.
      Throws:
      IOException

    • isMerged

      protected final boolean isMerged(SegmentInfos infos, SegmentCommitInfo info) throws IOException
      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
      Throws:
      IOException

    • getNoCFSRatio

      public final double getNoCFSRatio()
      Returns current noCFSRatio.
      See Also:

    • setNoCFSRatio

      public final void 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.

    • getMaxCFSSegmentSizeMB

      public final double getMaxCFSSegmentSizeMB()
      Returns the largest size allowed for a compound file segment

    • setMaxCFSSegmentSizeMB

      public final void setMaxCFSSegmentSizeMB(double v)
      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 Double.POSITIVE_INFINITY (default) and noCFSRatio to 1.0 to always use CFS regardless of merge size.