# Package org.apache.lucene.index

package org.apache.lucene.index
Code to maintain and access indices.

## Table Of Contents

1. Index APIs
   - IndexWriter
   - IndexReader
   - Segments and docids
2. Field types
   - Postings
   - Stored Fields
   - DocValues
   - Points
3. Postings APIs
   - Fields
   - Terms
   - Documents
   - Positions
4. Index Statistics
   - Term-level
   - Field-level
   - Segment-level
   - Document-level

## Index APIs

### IndexWriter

`IndexWriter` is used to create an index, and to add, update and delete documents. The IndexWriter class is thread safe, and enforces a single instance per index. Creating an IndexWriter creates a new index or opens an existing index for writing, in a `Directory`, depending on the configuration in `IndexWriterConfig`. A Directory is an abstraction that typically represents a local file-system directory (see various implementations of `FSDirectory`), but it may also stand for some other storage, such as RAM.

### IndexReader

`IndexReader` is used to read data from the index, and supports searching. Many thread-safe readers may be `DirectoryReader.open(org.apache.lucene.store.Directory)` concurrently with a single (or no) writer. Each reader maintains a consistent "point in time" view of an index and must be explicitly refreshed (see `DirectoryReader.openIfChanged(org.apache.lucene.index.DirectoryReader)`) in order to incorporate writes that may occur after it is opened.

### Segments and docids

Lucene's index is composed of segments, each of which contains a subset of all the documents in the index, and is a complete searchable index in itself, over that subset. As documents are written to the index, new segments are created and flushed to directory storage. Segments are immutable; updates and deletions may only create new segments and do not modify existing ones. Over time, the writer merges groups of smaller segments into single larger ones in order to maintain an index that is efficient to search, and to reclaim dead space left behind by deleted (and updated) documents.

Each document is identified by a 32-bit number, its "docid," and is composed of a collection of Field values of diverse types (postings, stored fields, doc values, and points). Docids come in two flavors: global and per-segment. A document's global docid is just the sum of its per-segment docid and that segment's base docid offset. External, high-level APIs only handle global docids, but internal APIs that reference a `LeafReader`, which is a reader for a single segment, deal in per-segment docids.

Docids are assigned sequentially within each segment (starting at 0). Thus the number of documents in a segment is the same as its maximum docid; some may be deleted, but their docids are retained until the segment is merged. When segments merge, their documents are assigned new sequential docids. Accordingly, docid values must always be treated as internal implementation, not exposed as part of an application, nor stored or referenced outside of Lucene's internal APIs.

## Field Types

Lucene supports a variety of different document field data structures. Lucene's core, the inverted index, is comprised of "postings." The postings, with their term dictionary, can be thought of as a map that provides efficient lookup given a `Term` (roughly, a word or token), to (the ordered list of) `Document`s containing that Term. Codecs may additionally record `impacts` alongside postings in order to be able to skip over low-scoring documents at search time. Postings do not provide any way of retrieving terms given a document, short of scanning the entire index.

Stored fields are essentially the opposite of postings, providing efficient retrieval of field values given a docid. All stored field values for a document are stored together in a block. Different types of stored field provide high-level datatypes such as strings and numbers on top of the underlying bytes. Stored field values are usually retrieved by the searcher using an implementation of `StoredFieldVisitor`.

`DocValues` fields are what are sometimes referred to as columnar, or column-stride fields, by analogy to relational database terminology, in which documents are considered as rows, and fields, columns. DocValues fields store values per-field: a value for every document is held in a single data structure, providing for rapid, sequential lookup of a field-value given a docid. These fields are used for efficient value-based sorting, and for faceting, but they are not useful for filtering.

`PointValues` represent numeric values using a kd-tree data structure. Efficient 1- and higher dimensional implementations make these the choice for numeric range and interval queries, and geo-spatial queries.

## Postings APIs

### Fields

`Fields` is the initial entry point into the postings APIs, this can be obtained in several ways:

     // access indexed fields for an index segment
     Fields fields = reader.fields();
     // access term vector fields for a specified document
     TermVectors vectors = reader.termVectors();
     Fields fields = vectors.get(docid);

Fields implements Java's Iterable interface, so it's easy to enumerate the list of fields:

     // enumerate list of fields
     for (String field : fields) {
       // access the terms for this field
       Terms terms = fields.terms(field);
     }

### Terms

`Terms` represents the collection of terms within a field, exposes some metadata and statistics, and an API for enumeration.

     // metadata about the field
     System.out.println("positions? " + terms.hasPositions());
     System.out.println("offsets? " + terms.hasOffsets());
     System.out.println("payloads? " + terms.hasPayloads());
     // iterate through terms
     TermsEnum termsEnum = terms.iterator(null);
     BytesRef term = null;
     while ((term = termsEnum.next()) != null) {
       doSomethingWith(termsEnum.term());
     }

`TermsEnum` provides an iterator over the list of terms within a field, some statistics about the term, and methods to access the term's documents and positions.

     // seek to a specific term
     boolean found = termsEnum.seekExact(new BytesRef("foobar"));
     if (found) {
       // get the document frequency
       System.out.println(termsEnum.docFreq());
       // enumerate through documents
       PostingsEnum docs = termsEnum.postings(null, null);
       // enumerate through documents and positions
       PostingsEnum docsAndPositions = termsEnum.postings(null, null, PostingsEnum.FLAG_POSITIONS);
     }

### Documents

`PostingsEnum` is an extension of `DocIdSetIterator`that iterates over the list of documents for a term, along with the term frequency within that document.

     int docid;
     while ((docid = docsEnum.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
       System.out.println(docid);
       System.out.println(docsEnum.freq());
      }

### Positions

PostingsEnum also allows iteration of the positions a term occurred within the document, and any additional per-position information (offsets and payload). The information available is controlled by flags passed to TermsEnum#postings

     int docid;
     PostingsEnum postings = termsEnum.postings(null, null, PostingsEnum.FLAG_PAYLOADS | PostingsEnum.FLAG_OFFSETS);
     while ((docid = postings.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
       System.out.println(docid);
       int freq = postings.freq();
       for (int i = 0; i < freq; i++) {
        System.out.println(postings.nextPosition());
        System.out.println(postings.startOffset());
        System.out.println(postings.endOffset());
        System.out.println(postings.getPayload());
       }
     }

## Index Statistics

### Term statistics

- `TermsEnum.docFreq()`: Returns the number of documents that contain at least one occurrence of the term. This statistic is always available for an indexed term. Note that it will also count deleted documents, when segments are merged the statistic is updated as those deleted documents are merged away.
- `TermsEnum.totalTermFreq()`: Returns the number of occurrences of this term across all documents. Like docFreq(), it will also count occurrences that appear in deleted documents.

### Field statistics

- `Terms.size()`: Returns the number of unique terms in the field. This statistic may be unavailable (returns `-1`) for some Terms implementations such as `MultiTerms`, where it cannot be efficiently computed. Note that this count also includes terms that appear only in deleted documents: when segments are merged such terms are also merged away and the statistic is then updated.
- `Terms.getDocCount()`: Returns the number of documents that contain at least one occurrence of any term for this field. This can be thought of as a Field-level docFreq(). Like docFreq() it will also count deleted documents.
- `Terms.getSumDocFreq()`: Returns the number of postings (term-document mappings in the inverted index) for the field. This can be thought of as the sum of `TermsEnum.docFreq()` across all terms in the field, and like docFreq() it will also count postings that appear in deleted documents.
- `Terms.getSumTotalTermFreq()`: Returns the number of tokens for the field. This can be thought of as the sum of `TermsEnum.totalTermFreq()` across all terms in the field, and like totalTermFreq() it will also count occurrences that appear in deleted documents.

### Segment statistics

- `IndexReader.maxDoc()`: Returns the number of documents (including deleted documents) in the index.
- `IndexReader.numDocs()`: Returns the number of live documents (excluding deleted documents) in the index.
- `IndexReader.numDeletedDocs()`: Returns the number of deleted documents in the index.
- `Fields.size()`: Returns the number of indexed fields.

### Document statistics

Document statistics are available during the indexing process for an indexed field: typically a `Similarity` implementation will store some of these values (possibly in a lossy way), into the normalization value for the document in its `Similarity.computeNorm(org.apache.lucene.index.FieldInvertState)` method.

- `FieldInvertState.getLength()`: Returns the number of tokens for this field in the document. Note that this is just the number of times that `TokenStream.incrementToken()` returned true, and is unrelated to the values in `PositionIncrementAttribute`.
- `FieldInvertState.getNumOverlap()`: Returns the number of tokens for this field in the document that had a position increment of zero. This can be used to compute a document length that discounts artificial tokens such as synonyms.
- `FieldInvertState.getPosition()`: Returns the accumulated position value for this field in the document: computed from the values of `PositionIncrementAttribute` and including `Analyzer.getPositionIncrementGap(java.lang.String)`s across multivalued fields.
- `FieldInvertState.getOffset()`: Returns the total character offset value for this field in the document: computed from the values of `OffsetAttribute` returned by `TokenStream.end()`, and including `Analyzer.getOffsetGap(java.lang.String)`s across multivalued fields.
- `FieldInvertState.getUniqueTermCount()`: Returns the number of unique terms encountered for this field in the document.
- `FieldInvertState.getMaxTermFrequency()`: Returns the maximum frequency across all unique terms encountered for this field in the document.

Additional user-supplied statistics can be added to the document as DocValues fields and accessed via `LeafReader.getNumericDocValues(java.lang.String)`.

Class
Description
AutomatonTermsEnum
A FilteredTermsEnum that enumerates terms based upon what is accepted by a DFA.
BaseCompositeReader<R extends IndexReader>
Base class for implementing `CompositeReader`s based on an array of sub-readers.
BaseTermsEnum
A base TermsEnum that adds default implementations for `BaseTermsEnum.attributes()` `BaseTermsEnum.termState()` `BaseTermsEnum.seekExact(BytesRef)` `BaseTermsEnum.seekExact(BytesRef, TermState)` In some cases, the default implementation may be slow and consume huge memory, so subclass SHOULD have its own implementation if possible.
BinaryDocValues
A per-document numeric value.
ByteVectorValues
This class provides access to per-document floating point vector values indexed as `KnnByteVectorField`.
CheckIndex
Basic tool and API to check the health of an index and write a new segments file that removes reference to problematic segments.
CheckIndex.CheckIndexException
The marker RuntimeException used by CheckIndex APIs when index integrity failure is detected.
CheckIndex.Level
Class with static variables with information about CheckIndex's -level parameter.
CheckIndex.Options
Run-time configuration options for CheckIndex commands.
CheckIndex.Status
Returned from `CheckIndex.checkIndex()` detailing the health and status of the index.
CheckIndex.Status.DocValuesStatus
Status from testing DocValues
CheckIndex.Status.FieldInfoStatus
Status from testing field infos.
CheckIndex.Status.FieldNormStatus
Status from testing field norms.
CheckIndex.Status.IndexSortStatus
Status from testing index sort
CheckIndex.Status.LiveDocStatus
Status from testing livedocs
CheckIndex.Status.PointsStatus
Status from testing PointValues
CheckIndex.Status.SegmentInfoStatus
Holds the status of each segment in the index.
CheckIndex.Status.SoftDeletesStatus
Status from testing soft deletes
CheckIndex.Status.StoredFieldStatus
Status from testing stored fields.
CheckIndex.Status.TermIndexStatus
Status from testing term index.
CheckIndex.Status.TermVectorStatus
Status from testing stored fields.
CheckIndex.Status.VectorValuesStatus
Status from testing vector values
CheckIndex.VerifyPointsVisitor
Walks the entire N-dimensional points space, verifying that all points fall within the last cell's boundaries.
CodecReader
LeafReader implemented by codec APIs.
CompositeReader
Instances of this reader type can only be used to get stored fields from the underlying LeafReaders, but it is not possible to directly retrieve postings.
CompositeReaderContext
`IndexReaderContext` for `CompositeReader` instance.
ConcurrentMergeScheduler
A `MergeScheduler` that runs each merge using a separate thread.
CorruptIndexException
This exception is thrown when Lucene detects an inconsistency in the index.
DirectoryReader
DirectoryReader is an implementation of `CompositeReader` that can read indexes in a `Directory`.
DocIDMerger<T extends DocIDMerger.Sub>
Utility class to help merging documents from sub-readers according to either simple concatenated (unsorted) order, or by a specified index-time sort, skipping deleted documents and remapping non-deleted documents.
DocIDMerger.Sub
Represents one sub-reader being merged
DocsWithFieldSet
Accumulator for documents that have a value for a field.
DocValues
This class contains utility methods and constants for DocValues
DocValuesSkipIndexType
Options for skip indexes on doc values.
DocValuesSkipper
Skipper for `DocValues`.
DocValuesType
DocValues types.
EmptyDocValuesProducer
Abstract base class implementing a `DocValuesProducer` that has no doc values.
ExitableDirectoryReader
The `ExitableDirectoryReader` wraps a real index `DirectoryReader` and allows for a `QueryTimeout` implementation object to be checked periodically to see if the thread should exit or not.
ExitableDirectoryReader.ExitableFilterAtomicReader
Wrapper class for another FilterAtomicReader.
ExitableDirectoryReader.ExitableSubReaderWrapper
Wrapper class for a SubReaderWrapper that is used by the ExitableDirectoryReader.
ExitableDirectoryReader.ExitableTerms
Wrapper class for another Terms implementation that is used by ExitableFields.
ExitableDirectoryReader.ExitableTermsEnum
Wrapper class for TermsEnum that is used by ExitableTerms for implementing an exitable enumeration of terms.
ExitableDirectoryReader.ExitingReaderException
Exception that is thrown to prematurely terminate a term enumeration.
FieldInfo
Access to the Field Info file that describes document fields and whether or not they are indexed.
FieldInfos
Collection of `FieldInfo`s (accessible by number or by name).
FieldInvertState
This class tracks the number and position / offset parameters of terms being added to the index.
Fields
Provides a `Terms` index for fields that have it, and lists which fields do.
FilterBinaryDocValues
Delegates all methods to a wrapped `BinaryDocValues`.
FilterCodecReader
A `FilterCodecReader` contains another CodecReader, which it uses as its basic source of data, possibly transforming the data along the way or providing additional functionality.
FilterDirectoryReader
A FilterDirectoryReader wraps another DirectoryReader, allowing implementations to transform or extend it.
FilterDirectoryReader.DelegatingCacheHelper
A DelegatingCacheHelper is a CacheHelper specialization for implementing long-lived caching behaviour for FilterDirectoryReader subclasses.
FilterDirectoryReader.SubReaderWrapper
Factory class passed to FilterDirectoryReader constructor that allows subclasses to wrap the filtered DirectoryReader's subreaders.
FilteredTermsEnum
Abstract class for enumerating a subset of all terms.
FilteredTermsEnum.AcceptStatus
Return value, if term should be accepted or the iteration should `END`.
FilterLeafReader
A `FilterLeafReader` contains another LeafReader, which it uses as its basic source of data, possibly transforming the data along the way or providing additional functionality.
FilterLeafReader.FilterFields
Base class for filtering `Fields` implementations.
FilterLeafReader.FilterPostingsEnum
Base class for filtering `PostingsEnum` implementations.
FilterLeafReader.FilterTerms
Base class for filtering `Terms` implementations.
FilterLeafReader.FilterTermsEnum
Base class for filtering `TermsEnum` implementations.
FilterMergePolicy
A wrapper for `MergePolicy` instances.
FilterNumericDocValues
Delegates all methods to a wrapped `NumericDocValues`.
FilterSortedDocValues
Delegates all methods to a wrapped `SortedDocValues`.
FilterSortedNumericDocValues
Delegates all methods to a wrapped `SortedNumericDocValues`.
FilterSortedSetDocValues
Delegates all methods to a wrapped `SortedSetDocValues`.
FloatVectorValues
This class provides access to per-document floating point vector values indexed as `KnnFloatVectorField`.
Impact
Per-document scoring factors.
Impacts
Information about upcoming impacts, ie.
ImpactsEnum
Extension of `PostingsEnum` which also provides information about upcoming impacts.
ImpactsSource
Source of `Impacts`.
IndexableField
Represents a single field for indexing.
IndexableFieldType
Describes the properties of a field.
IndexCommit
Expert: represents a single commit into an index as seen by the `IndexDeletionPolicy` or `IndexReader`.
IndexDeletionPolicy
Expert: policy for deletion of stale `index commits`.
IndexFileNames
This class contains useful constants representing filenames and extensions used by lucene, as well as convenience methods for querying whether a file name matches an extension (`matchesExtension`), as well as generating file names from a segment name, generation and extension ( `fileNameFromGeneration`, `segmentFileName`).
IndexFormatTooNewException
This exception is thrown when Lucene detects an index that is newer than this Lucene version.
IndexFormatTooOldException
This exception is thrown when Lucene detects an index that is too old for this Lucene version
IndexNotFoundException
Signals that no index was found in the Directory.
IndexOptions
Controls how much information is stored in the postings lists.
IndexReader
IndexReader is an abstract class, providing an interface for accessing a point-in-time view of an index.
IndexReader.CacheHelper
A utility class that gives hooks in order to help build a cache based on the data that is contained in this index.
IndexReader.CacheKey
A cache key identifying a resource that is being cached on.
IndexReader.ClosedListener
A listener that is called when a resource gets closed.
IndexReaderContext
A struct like class that represents a hierarchical relationship between `IndexReader` instances.
IndexSorter
Handles how documents should be sorted in an index, both within a segment and between segments.
IndexSorter.ComparableProvider
Used for sorting documents across segments
IndexSorter.DocComparator
A comparator of doc IDs, used for sorting documents within a segment
IndexSorter.DoubleSorter
Sorts documents based on double values from a NumericDocValues instance
IndexSorter.FloatSorter
Sorts documents based on float values from a NumericDocValues instance
IndexSorter.IntSorter
Sorts documents based on integer values from a NumericDocValues instance
IndexSorter.LongSorter
Sorts documents based on long values from a NumericDocValues instance
IndexSorter.NumericDocValuesProvider
Provide a NumericDocValues instance for a LeafReader
IndexSorter.SortedDocValuesProvider
Provide a SortedDocValues instance for a LeafReader
IndexSorter.StringSorter
Sorts documents based on terms from a SortedDocValues instance
IndexUpgrader
This is an easy-to-use tool that upgrades all segments of an index from previous Lucene versions to the current segment file format.
IndexWriter
An `IndexWriter` creates and maintains an index.
IndexWriter.DocStats
DocStats for this index
IndexWriter.IndexReaderWarmer
If `DirectoryReader.open(IndexWriter)` has been called (ie, this writer is in near real-time mode), then after a merge completes, this class can be invoked to warm the reader on the newly merged segment, before the merge commits.
IndexWriterConfig
Holds all the configuration that is used to create an `IndexWriter`.
IndexWriterConfig.OpenMode
Specifies the open mode for `IndexWriter`.
IndexWriterEventListener
A callback event listener for recording key events happened inside IndexWriter
KeepOnlyLastCommitDeletionPolicy
This `IndexDeletionPolicy` implementation that keeps only the most recent commit and immediately removes all prior commits after a new commit is done.
KnnVectorValues
This class abstracts addressing of document vector values indexed as `KnnFloatVectorField` or `KnnByteVectorField`.
KnnVectorValues.DocIndexIterator
A DocIdSetIterator that also provides an index() method tracking a distinct ordinal for a vector associated with each doc.
LeafMetaData
Provides read-only metadata about a leaf.
LeafReader
`LeafReader` is an abstract class, providing an interface for accessing an index.
LeafReaderContext
`IndexReaderContext` for `LeafReader` instances.
LiveIndexWriterConfig
Holds all the configuration used by `IndexWriter` with few setters for settings that can be changed on an `IndexWriter` instance "live".
LogByteSizeMergePolicy
This is a `LogMergePolicy` that measures size of a segment as the total byte size of the segment's files.
LogDocMergePolicy
This is a `LogMergePolicy` that measures size of a segment as the number of documents (not taking deletions into account).
LogMergePolicy
This class implements a `MergePolicy` that tries to merge segments into levels of exponentially increasing size, where each level has fewer segments than the value of the merge factor.
MappedMultiFields
A `Fields` implementation that merges multiple Fields into one, and maps around deleted documents.
MergePolicy
Expert: a MergePolicy determines the sequence of primitive merge operations.
MergePolicy.MergeAbortedException
Thrown when a merge was explicitly aborted because `IndexWriter.abortMerges()` was called.
MergePolicy.MergeContext
This interface represents the current context of the merge selection process.
MergePolicy.MergeException
Exception thrown if there are any problems while executing a merge.
MergePolicy.MergeSpecification
A MergeSpecification instance provides the information necessary to perform multiple merges.
MergePolicy.OneMerge
OneMerge provides the information necessary to perform an individual primitive merge operation, resulting in a single new segment.
MergePolicy.OneMergeProgress
Progress and state for an executing merge.
MergePolicy.OneMergeProgress.PauseReason
Reason for pausing the merge thread.
MergeRateLimiter
This is the `RateLimiter` that `IndexWriter` assigns to each running merge, to give `MergeScheduler`s ionice like control.
MergeScheduler
Expert: `IndexWriter` uses an instance implementing this interface to execute the merges selected by a `MergePolicy`.
MergeScheduler.MergeSource
Provides access to new merges and executes the actual merge
MergeState
Holds common state used during segment merging.
MergeState.DocMap
A map of doc IDs.
MergeTrigger
MergeTrigger is passed to `MergePolicy.findMerges(MergeTrigger, SegmentInfos, MergePolicy.MergeContext)` to indicate the event that triggered the merge.
MultiBits
Concatenates multiple Bits together, on every lookup.
MultiDocValues
A wrapper for CompositeIndexReader providing access to DocValues.
MultiDocValues.MultiSortedDocValues
Implements SortedDocValues over n subs, using an OrdinalMap
MultiDocValues.MultiSortedSetDocValues
Implements MultiSortedSetDocValues over n subs, using an OrdinalMap
MultiFields
Provides a single `Fields` term index view over an `IndexReader`.
MultiLeafReader
Utility methods for working with a `IndexReader` as if it were a `LeafReader`.
MultiPostingsEnum
Exposes `PostingsEnum`, merged from `PostingsEnum` API of sub-segments.
MultiPostingsEnum.EnumWithSlice
Holds a `PostingsEnum` along with the corresponding `ReaderSlice`.
MultiReader
A `CompositeReader` which reads multiple indexes, appending their content.
MultiTerms
Exposes flex API, merged from flex API of sub-segments.
MultiTermsEnum
Exposes `TermsEnum` API, merged from `TermsEnum` API of sub-segments.
NoDeletionPolicy
An `IndexDeletionPolicy` which keeps all index commits around, never deleting them.
NoMergePolicy
A `MergePolicy` which never returns merges to execute.
NoMergeScheduler
A `MergeScheduler` which never executes any merges.
NumericDocValues
A per-document numeric value.
OneMergeWrappingMergePolicy
A wrapping merge policy that wraps the `MergePolicy.OneMerge` objects returned by the wrapped merge policy.
OrdinalMap
Maps per-segment ordinals to/from global ordinal space, using a compact packed-ints representation.
OrdTermState
An ordinal based `TermState`
ParallelCompositeReader
An `CompositeReader` which reads multiple, parallel indexes.
ParallelLeafReader
An `LeafReader` which reads multiple, parallel indexes.
PersistentSnapshotDeletionPolicy
A `SnapshotDeletionPolicy` which adds a persistence layer so that snapshots can be maintained across the life of an application.
PointValues
Access to indexed numeric values.
PointValues.IntersectVisitor
We recurse the `PointValues.PointTree`, using a provided instance of this to guide the recursion.
PointValues.PointTree
Basic operations to read the KD-tree.
PointValues.Relation
Used by `PointValues.intersect(org.apache.lucene.index.PointValues.IntersectVisitor)` to check how each recursive cell corresponds to the query.
PostingsEnum
Iterates through the postings.
PrefixCodedTerms
Prefix codes term instances (prefixes are shared).
PrefixCodedTerms.Builder
Builds a PrefixCodedTerms: call add repeatedly, then finish.
PrefixCodedTerms.TermIterator
An iterator over the list of terms stored in a `PrefixCodedTerms`.
QueryTimeout
Query timeout abstraction that controls whether a query should continue or be stopped.
QueryTimeoutImpl
An implementation of `QueryTimeout` that can be used by the `ExitableDirectoryReader` class to time out and exit out when a query takes a long time to rewrite.
ReaderManager
Utility class to safely share `DirectoryReader` instances across multiple threads, while periodically reopening.
ReaderSlice
Subreader slice from a parent composite reader.
ReaderUtil
Common util methods for dealing with `IndexReader`s and `IndexReaderContext`s.
SegmentCommitInfo
Embeds a [read-only] SegmentInfo and adds per-commit fields.
SegmentInfo
Information about a segment such as its name, directory, and files related to the segment.
SegmentInfos
A collection of segmentInfo objects with methods for operating on those segments in relation to the file system.
SegmentInfos.FindSegmentsFile<T>
Utility class for executing code that needs to do something with the current segments file.
SegmentReader
IndexReader implementation over a single segment.
SegmentReadState
Holder class for common parameters used during read.
SegmentWriteState
Holder class for common parameters used during write.
SerialMergeScheduler
A `MergeScheduler` that simply does each merge sequentially, using the current thread.
SimpleMergedSegmentWarmer
A very simple merged segment warmer that just ensures data structures are initialized.
SingleTermsEnum
Subclass of FilteredTermsEnum for enumerating a single term.
SlowCodecReaderWrapper
Wraps arbitrary readers for merging.
SlowImpactsEnum
`ImpactsEnum` that doesn't index impacts but implements the API in a legal way.
SnapshotDeletionPolicy
An `IndexDeletionPolicy` that wraps any other `IndexDeletionPolicy` and adds the ability to hold and later release snapshots of an index.
SoftDeletesDirectoryReaderWrapper
This reader filters out documents that have a doc values value in the given field and treat these documents as soft deleted.
SoftDeletesRetentionMergePolicy
This `MergePolicy` allows to carry over soft deleted documents across merges.
SortedDocValues
A per-document byte[] with presorted values.
SortedNumericDocValues
A list of per-document numeric values, sorted according to `Long.compare(long, long)`.
SortedSetDocValues
A multi-valued version of `SortedDocValues`.
Sorter
Sorts documents of a given index by returning a permutation on the document IDs.
Sorter.DocMap
A permutation of doc IDs.
SortFieldProvider
Reads/Writes a named SortField from a segment info file, used to record index sorts
SortingCodecReader
An `CodecReader` which supports sorting documents by a given `Sort`.
SortingCodecReader.SortingValuesIterator
Iterator over KnnVectorValues accepting a mapping to differently-sorted docs.
StandardDirectoryReader
Default implementation of `DirectoryReader`.
StoredFields
API for reading stored fields.
StoredFieldVisitor
Expert: provides a low-level means of accessing the stored field values in an index.
StoredFieldVisitor.Status
Enumeration of possible return values for `StoredFieldVisitor.needsField(org.apache.lucene.index.FieldInfo)`.
Term
A Term represents a word from text.
Terms
Access to the terms in a specific field.
TermsEnum
Iterator to seek (`TermsEnum.seekCeil(BytesRef)`, `TermsEnum.seekExact(BytesRef)`) or step through (`BytesRefIterator.next()` terms to obtain frequency information (`TermsEnum.docFreq()`), `PostingsEnum` or `PostingsEnum` for the current term (`TermsEnum.postings(org.apache.lucene.index.PostingsEnum)`.
TermsEnum.SeekStatus
Represents returned result from `TermsEnum.seekCeil(org.apache.lucene.util.BytesRef)`.
TermState
Encapsulates all required internal state to position the associated `TermsEnum` without re-seeking.
TermStates
Maintains a `IndexReader` `TermState` view over `IndexReader` instances containing a single term.
TermVectors
API for reading term vectors.
TieredMergePolicy
Merges segments of approximately equal size, subject to an allowed number of segments per tier.
TieredMergePolicy.MergeScore
Holds score and explanation for a single candidate merge.
TwoPhaseCommit
An interface for implementations that support 2-phase commit.
TwoPhaseCommitTool
A utility for executing 2-phase commit on several objects.
TwoPhaseCommitTool.CommitFailException
Thrown by `TwoPhaseCommitTool.execute(TwoPhaseCommit...)` when an object fails to commit().
TwoPhaseCommitTool.PrepareCommitFailException
Thrown by `TwoPhaseCommitTool.execute(TwoPhaseCommit...)` when an object fails to prepareCommit().
UpgradeIndexMergePolicy
This `MergePolicy` is used for upgrading all existing segments of an index when calling `IndexWriter.forceMerge(int)`.
VectorEncoding
The numeric datatype of the vector values.
VectorSimilarityFunction
Vector similarity function; used in search to return top K most similar vectors to a target vector.