org.apache.lucene.index

## Class SegmentInfos

- java.lang.Object
- - org.apache.lucene.index.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.

  Files:

  - `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.

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static class` | `SegmentInfos.FindSegmentsFile<T>` Utility class for executing code that needs to do something with the current segments file.

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `long` | `counter` Used to name new segments.
    `Map<String,String>` | `userData` Opaque Map<String, String> that user can specify during IndexWriter.commit
    `long` | `version` Counts how often the index has been changed.
    `static int` | `VERSION_70` The version that added information about the Lucene version at the time when the index has been created.
    `static int` | `VERSION_72` The version that updated segment name counter to be long instead of int.
    `static int` | `VERSION_74` The version that recorded softDelCount

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `SegmentInfos(int indexCreatedVersionMajor)` Sole constructor.

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `add(SegmentCommitInfo si)` Appends the provided `SegmentCommitInfo`.
    `void` | `addAll(Iterable<SegmentCommitInfo> sis)` Appends the provided `SegmentCommitInfo`s.
    `List<SegmentCommitInfo>` | `asList()` Returns all contained segments as an unmodifiable `List` view.
    `void` | `changed()` Call this before committing if changes have been made to the segments.
    `void` | `clear()` Clear all `SegmentCommitInfo`s.
    `SegmentInfos` | `clone()` Returns a copy of this instance, also copying each SegmentInfo.
    `void` | `commit(Directory dir)` Writes and syncs to the Directory dir, taking care to remove the segments file on exception
    `Collection<String>` | `files(boolean includeSegmentsFile)` Returns all file names referenced by SegmentInfo.
    `static long` | `generationFromSegmentsFileName(String fileName)` Parse the generation off the segments file name and return it.
    `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.
    `long` | `getGeneration()` Returns current generation.
    `byte[]` | `getId()` Since Lucene 5.0, every commit (segments_N) writes a unique id.
    `int` | `getIndexCreatedVersionMajor()` Return the version major that was used to initially create the index.
    `static PrintStream` | `getInfoStream()` Returns `infoStream`.
    `static long` | `getLastCommitGeneration(Directory directory)` Get the generation of the most recent commit to the index in this directory (N in the segments_N file).
    `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).
    `static String` | `getLastCommitSegmentsFileName(Directory directory)` Get the filename of the segments_N file for the most recent commit to the index in this Directory.
    `static String` | `getLastCommitSegmentsFileName(String[] files)` Get the filename of the segments_N file for the most recent commit in the list of index files.
    `long` | `getLastGeneration()` Returns last succesfully read or written generation.
    `Version` | `getMinSegmentLuceneVersion()` Returns the version of the oldest segment, or null if there are no segments.
    `String` | `getSegmentsFileName()` Get the segments_N filename in use by this segment infos.
    `Map<String,String>` | `getUserData()` Return `userData` saved with this commit.
    `long` | `getVersion()` version number when this SegmentInfos was generated.
    `SegmentCommitInfo` | `info(int i)` Returns `SegmentCommitInfo` at the provided index.
    `Iterator<SegmentCommitInfo>` | `iterator()` Returns an unmodifiable `Iterator` of contained segments in order.
    `static SegmentInfos` | `readCommit(Directory directory, ChecksumIndexInput input, long generation)` Read the commit from the provided `ChecksumIndexInput`.
    `static SegmentInfos` | `readCommit(Directory directory, String segmentFileName)` Read a particular segmentFileName.
    `static SegmentInfos` | `readLatestCommit(Directory directory)` Find the latest commit (`segments_N file`) and load all `SegmentCommitInfo`s.
    `boolean` | `remove(SegmentCommitInfo si)` Remove the provided `SegmentCommitInfo`.
    `static void` | `setInfoStream(PrintStream infoStream)` If non-null, information about retries when loading the segments file will be printed to this.
    `void` | `setNextWriteGeneration(long generation)` Set the generation to be used for the next commit
    `void` | `setUserData(Map<String,String> data, boolean doIncrementVersion)` Sets the commit data.
    `int` | `size()` Returns number of `SegmentCommitInfo`s.
    `String` | `toString()` Returns readable description of this segment.
    `int` | `totalMaxDoc()` Returns sum of all segment's maxDocs.
    `void` | `updateGeneration(SegmentInfos other)` Carry over generation numbers from another SegmentInfos
    `void` | `write(Directory directory, IndexOutput out)` Write ourselves to the provided `IndexOutput`

    - ### Methods inherited from class java.lang.Object

      `equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

    - ### Methods inherited from interface java.lang.Iterable

      `forEach, spliterator`

- - ### Field Detail

    - #### 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:
        Constant Field Values

    - #### VERSION_72

          public static final int VERSION_72

      The version that updated segment name counter to be long instead of int.
      See Also:
        Constant Field Values

    - #### VERSION_74

          public static final int VERSION_74

      The version that recorded softDelCount
      See Also:
        Constant Field Values

    - #### 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 Detail

    - #### SegmentInfos

          public SegmentInfos(int indexCreatedVersionMajor)

      Sole constructor.
      Parameters:
        `indexCreatedVersionMajor` - the Lucene version major at index creation time, or 6 if the index was created before 7.0

  - ### Method Detail

    - #### 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).
      Parameters:
        `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).
      Parameters:
        `directory` - -- directory to search for the latest segments_N file
      Throws:
        `IOException`

    - #### 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.
      Parameters:
        `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.
      Parameters:
        `directory` - -- directory to search for the latest segments_N file
      Throws:
        `IOException`

    - #### 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.
      Parameters:
        `directory` - -- directory containing the segments file
        `segmentFileName` - -- segment file to load
      Throws:
        `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`.
      Throws:
        `IOException`

    - #### readLatestCommit

          public static final SegmentInfos readLatestCommit(Directory directory)
                                                     throws IOException

      Find the latest commit (`segments_N file`) and load all `SegmentCommitInfo`s.
      Throws:
        `IOException`

    - #### write

          public void write(Directory directory,
                            IndexOutput out)
                     throws IOException

      Write ourselves to the provided `IndexOutput`
      Throws:
        `IOException`

    - #### clone

          public SegmentInfos clone()

      Returns a copy of this instance, also copying each SegmentInfo.
      Overrides:
        `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:
        `setInfoStream(java.io.PrintStream)`

    - #### 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.
      Throws:
        `IOException`

    - #### 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

      Throws:
        `IOException`

    - #### toString

          public String toString()

      Returns readable description of this segment.
      Overrides:
        `toString` in class `Object`

    - #### getUserData

          public Map<String,String> getUserData()

      Return `userData` saved with this commit.
      See Also:
        `IndexWriter.commit()`

    - #### 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 `SegmentCommitInfo`s.

    - #### add

          public void add(SegmentCommitInfo si)

      Appends the provided `SegmentCommitInfo`.

    - #### addAll

          public void addAll(Iterable<SegmentCommitInfo> sis)

      Appends the provided `SegmentCommitInfo`s.

    - #### clear

          public void clear()

      Clear all `SegmentCommitInfo`s.

    - #### 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.

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