Class SegmentInfos

All Implemented Interfaces:
Cloneable, Iterable<SegmentCommitInfo>

public final class SegmentInfos extends Object implements Cloneable, Iterable<SegmentCommitInfo>
A collection of segmentInfo objects with methods for operating on those segments in relation to the file system.

The active segments in the index are stored in the segment info file, segments_N. There may be one or more segments_N files in the index; however, the one with the largest generation is the active one (when older segments_N files are present it's because they temporarily cannot be deleted, or a custom IndexDeletionPolicy is in use). This file lists each segment by name and has details about the codec and generation of deletes.


  • segments_N: Header, LuceneVersion, Version, NameCounter, SegCount, MinSegmentLuceneVersion, <SegName, SegID, SegCodec, DelGen, DeletionCount, FieldInfosGen, DocValuesGen, UpdatesFiles>SegCount, CommitUserData, Footer
Data types:
  • Header --> IndexHeader
  • LuceneVersion --> Which Lucene code Version was used for this commit, written as three vInt: major, minor, bugfix
  • MinSegmentLuceneVersion --> Lucene code Version of the oldest segment, written as three vInt: major, minor, bugfix; this is only written only if there's at least one segment
  • NameCounter, SegCount, DeletionCount --> Int32
  • Generation, Version, DelGen, Checksum, FieldInfosGen, DocValuesGen --> Int64
  • SegID --> Int8ID_LENGTH
  • SegName, SegCodec --> String
  • CommitUserData --> Map<String,String>
  • UpdatesFiles --> Map<Int32, Set<String>>
  • Footer --> CodecFooter
Field Descriptions:
  • Version counts how often the index has been changed by adding or deleting documents.
  • NameCounter is used to generate names for new segment files.
  • SegName is the name of the segment, and is used as the file name prefix for all of the files that compose the segment's index.
  • DelGen is the generation count of the deletes file. If this is -1, there are no deletes. Anything above zero means there are deletes stored by LiveDocsFormat.
  • DeletionCount records the number of deleted documents in this segment.
  • SegCodec is the name of the Codec that encoded this segment.
  • SegID is the identifier of the Codec that encoded this segment.
  • CommitUserData stores an optional user-supplied opaque Map<String,String> that was passed to IndexWriter.setLiveCommitData(Iterable).
  • FieldInfosGen is the generation count of the fieldInfos file. If this is -1, there are no updates to the fieldInfos in that segment. Anything above zero means there are updates to fieldInfos stored by FieldInfosFormat .
  • DocValuesGen is the generation count of the updatable DocValues. If this is -1, there are no updates to DocValues in that segment. Anything above zero means there are updates to DocValues stored by DocValuesFormat.
  • UpdatesFiles stores the set of files that were updated in that segment per field.
WARNING: This API is experimental and might change in incompatible ways in the next release.
  • Field Details

    • VERSION_70

      public static final int VERSION_70
      The version that added information about the Lucene version at the time when the index has been created.
      See Also:
    • VERSION_72

      public static final int VERSION_72
      The version that updated segment name counter to be long instead of int.
      See Also:
    • VERSION_74

      public static final int VERSION_74
      The version that recorded softDelCount
      See Also:
    • VERSION_86

      public static final int VERSION_86
      The version that recorded SegmentCommitInfo IDs
      See Also:
    • counter

      public long counter
      Used to name new segments.
    • version

      public long version
      Counts how often the index has been changed.
    • userData

      public Map<String,String> userData
      Opaque Map<String, String> that user can specify during IndexWriter.commit
  • Constructor Details

    • SegmentInfos

      public SegmentInfos(int indexCreatedVersionMajor)
      Sole constructor.
      indexCreatedVersionMajor - the Lucene version major at index creation time, or 6 if the index was created before 7.0
  • Method Details

    • info

      public SegmentCommitInfo info(int i)
      Returns SegmentCommitInfo at the provided index.
    • getLastCommitGeneration

      public static long getLastCommitGeneration(String[] files)
      Get the generation of the most recent commit to the list of index files (N in the segments_N file).
      files - -- array of file names to check
    • getLastCommitGeneration

      public static long getLastCommitGeneration(Directory directory) throws IOException
      Get the generation of the most recent commit to the index in this directory (N in the segments_N file).
      directory - -- directory to search for the latest segments_N file
    • getLastCommitSegmentsFileName

      public static String getLastCommitSegmentsFileName(String[] files)
      Get the filename of the segments_N file for the most recent commit in the list of index files.
      files - -- array of file names to check
    • getLastCommitSegmentsFileName

      public static String getLastCommitSegmentsFileName(Directory directory) throws IOException
      Get the filename of the segments_N file for the most recent commit to the index in this Directory.
      directory - -- directory to search for the latest segments_N file
    • getSegmentsFileName

      public String getSegmentsFileName()
      Get the segments_N filename in use by this segment infos.
    • generationFromSegmentsFileName

      public static long generationFromSegmentsFileName(String fileName)
      Parse the generation off the segments file name and return it.
    • getId

      public byte[] getId()
      Since Lucene 5.0, every commit (segments_N) writes a unique id. This will return that id
    • readCommit

      public static final SegmentInfos readCommit(Directory directory, String segmentFileName) throws IOException
      Read a particular segmentFileName. Note that this may throw an IOException if a commit is in process.
      directory - -- directory containing the segments file
      segmentFileName - -- segment file to load
      CorruptIndexException - if the index is corrupt
      IOException - if there is a low-level IO error
    • readCommit

      public static final SegmentInfos readCommit(Directory directory, ChecksumIndexInput input, long generation) throws IOException
      Read the commit from the provided ChecksumIndexInput.
    • readLatestCommit

      public static final SegmentInfos readLatestCommit(Directory directory) throws IOException
      Find the latest commit (segments_N file) and load all SegmentCommitInfos.
    • write

      public void write(IndexOutput out) throws IOException
      Write ourselves to the provided IndexOutput
    • clone

      public SegmentInfos clone()
      Returns a copy of this instance, also copying each SegmentInfo.
      clone in class Object
    • getVersion

      public long getVersion()
      version number when this SegmentInfos was generated.
    • getGeneration

      public long getGeneration()
      Returns current generation.
    • getLastGeneration

      public long getLastGeneration()
      Returns last succesfully read or written generation.
    • setInfoStream

      public static void setInfoStream(PrintStream infoStream)
      If non-null, information about retries when loading the segments file will be printed to this.
    • getInfoStream

      public static PrintStream getInfoStream()
      Returns infoStream.
      See Also:
    • updateGeneration

      public void updateGeneration(SegmentInfos other)
      Carry over generation numbers from another SegmentInfos
      NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.
    • setNextWriteGeneration

      public void setNextWriteGeneration(long generation)
      Set the generation to be used for the next commit
    • files

      public Collection<String> files(boolean includeSegmentsFile) throws IOException
      Returns all file names referenced by SegmentInfo. The returned collection is recomputed on each invocation.
    • commit

      public final void commit(Directory dir) throws IOException
      Writes and syncs to the Directory dir, taking care to remove the segments file on exception

      Note: changed() should be called prior to this method if changes have been made to this SegmentInfos instance

    • toString

      public String toString()
      Returns readable description of this segment.
      toString in class Object
    • getUserData

      public Map<String,String> getUserData()
      Return userData saved with this commit.
      See Also:
    • setUserData

      public void setUserData(Map<String,String> data, boolean doIncrementVersion)
      Sets the commit data.
    • totalMaxDoc

      public int totalMaxDoc()
      Returns sum of all segment's maxDocs. Note that this does not include deletions
    • changed

      public void changed()
      Call this before committing if changes have been made to the segments.
    • iterator

      public Iterator<SegmentCommitInfo> iterator()
      Returns an unmodifiable Iterator of contained segments in order.
      Specified by:
      iterator in interface Iterable<SegmentCommitInfo>
    • asList

      public List<SegmentCommitInfo> asList()
      Returns all contained segments as an unmodifiable List view.
    • size

      public int size()
      Returns number of SegmentCommitInfos.
    • add

      public void add(SegmentCommitInfo si)
      Appends the provided SegmentCommitInfo.
    • addAll

      public void addAll(Iterable<SegmentCommitInfo> sis)
      Appends the provided SegmentCommitInfos.
    • clear

      public void clear()
      Clear all SegmentCommitInfos.
    • remove

      public boolean remove(SegmentCommitInfo si)
      Remove the provided SegmentCommitInfo.

      WARNING: O(N) cost

    • getCommitLuceneVersion

      public Version getCommitLuceneVersion()
      Returns which Lucene Version wrote this commit, or null if the version this index was written with did not directly record the version.
    • getMinSegmentLuceneVersion

      public Version getMinSegmentLuceneVersion()
      Returns the version of the oldest segment, or null if there are no segments.
    • getIndexCreatedVersionMajor

      public int getIndexCreatedVersionMajor()
      Return the version major that was used to initially create the index. This version is set when the index is first created and then never changes. This information was added as of version 7.0 so older indices report 6 as a creation version.