mayya-sharipova commented on code in PR #14078: URL: https://github.com/apache/lucene/pull/14078#discussion_r1890778000
########## lucene/core/src/java/org/apache/lucene/codecs/lucene102/package-info.java: ########## @@ -0,0 +1,436 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +/** + * Lucene 10.2 file format. + * + * <h2>Apache Lucene - Index File Formats</h2> + * + * <div> + * + * <ul> + * <li><a href="#Introduction">Introduction</a> + * <li><a href="#Definitions">Definitions</a> + * <ul> + * <li><a href="#Inverted_Indexing">Inverted Indexing</a> + * <li><a href="#Types_of_Fields">Types of Fields</a> + * <li><a href="#Segments">Segments</a> + * <li><a href="#Document_Numbers">Document Numbers</a> + * </ul> + * <li><a href="#Overview">Index Structure Overview</a> + * <li><a href="#File_Naming">File Naming</a> + * <li><a href="#file-names">Summary of File Extensions</a> + * <ul> + * <li><a href="#Lock_File">Lock File</a> + * <li><a href="#History">History</a> + * <li><a href="#Limitations">Limitations</a> + * </ul> + * </ul> + * + * </div> <a id="Introduction"></a> + * + * <h3>Introduction</h3> + * + * <div> + * + * <p>This document defines the index file formats used in this version of Lucene. If you are using + * a different version of Lucene, please consult the copy of <code>docs/</code> that was distributed + * with the version you are using. + * + * <p>This document attempts to provide a high-level definition of the Apache Lucene file formats. + * </div> <a id="Definitions"></a> + * + * <h3>Definitions</h3> + * + * <div> + * + * <p>The fundamental concepts in Lucene are index, document, field and term. + * + * <p>An index contains a sequence of documents. + * + * <ul> + * <li>A document is a sequence of fields. + * <li>A field is a named sequence of terms. + * <li>A term is a sequence of bytes. + * </ul> + * + * <p>The same sequence of bytes in two different fields is considered a different term. Thus terms + * are represented as a pair: the string naming the field, and the bytes within the field. <a + * id="Inverted_Indexing"></a> + * + * <h4>Inverted Indexing</h4> + * + * <p>Lucene's index stores terms and statistics about those terms in order to make term-based + * search more efficient. Lucene's terms index falls into the family of indexes known as an + * <i>inverted index.</i> This is because it can list, for a term, the documents that contain it. + * This is the inverse of the natural relationship, in which documents list terms. <a + * id="Types_of_Fields"></a> + * + * <h4>Types of Fields</h4> + * + * <p>In Lucene, fields may be <i>stored</i>, in which case their text is stored in the index + * literally, in a non-inverted manner. Fields that are inverted are called <i>indexed</i>. A field + * may be both stored and indexed. + * + * <p>The text of a field may be <i>tokenized</i> into terms to be indexed, or the text of a field + * may be used literally as a term to be indexed. Most fields are tokenized, but sometimes it is + * useful for certain identifier fields to be indexed literally. + * + * <p>See the {@link org.apache.lucene.document.Field Field} java docs for more information on + * Fields. <a id="Segments"></a> + * + * <h4>Segments</h4> + * + * <p>Lucene indexes may be composed of multiple sub-indexes, or <i>segments</i>. Each segment is a + * fully independent index, which could be searched separately. Indexes evolve by: + * + * <ol> + * <li>Creating new segments for newly added documents. + * <li>Merging existing segments. + * </ol> + * + * <p>Searches may involve multiple segments and/or multiple indexes, each index potentially + * composed of a set of segments. <a id="Document_Numbers"></a> + * + * <h4>Document Numbers</h4> + * + * <p>Internally, Lucene refers to documents by an integer <i>document number</i>. The first + * document added to an index is numbered zero, and each subsequent document added gets a number one + * greater than the previous. + * + * <p>Note that a document's number may change, so caution should be taken when storing these + * numbers outside of Lucene. In particular, numbers may change in the following situations: + * + * <ul> + * <li> + * <p>The numbers stored in each segment are unique only within the segment, and must be + * converted before they can be used in a larger context. The standard technique is to + * allocate each segment a range of values, based on the range of numbers used in that + * segment. To convert a document number from a segment to an external value, the segment's + * <i>base</i> document number is added. To convert an external value back to a + * segment-specific value, the segment is identified by the range that the external value is + * in, and the segment's base value is subtracted. For example two five document segments + * might be combined, so that the first segment has a base value of zero, and the second of + * five. Document three from the second segment would have an external value of eight. + * <li> + * <p>When documents are deleted, gaps are created in the numbering. These are eventually + * removed as the index evolves through merging. Deleted documents are dropped when segments + * are merged. A freshly-merged segment thus has no gaps in its numbering. + * </ul> + * + * </div> <a id="Overview"></a> + * + * <h3>Index Structure Overview</h3> + * + * <div> + * + * <p>Each segment index maintains the following: + * + * <ul> + * <li>{@link org.apache.lucene.codecs.lucene99.Lucene99SegmentInfoFormat Segment info}. This + * contains metadata about a segment, such as the number of documents, what files it uses, and + * information about how the segment is sorted + * <li>{@link org.apache.lucene.codecs.lucene94.Lucene94FieldInfosFormat Field names}. This + * contains metadata about the set of named fields used in the index. + * <li>{@link org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat Stored Field values}. + * This contains, for each document, a list of attribute-value pairs, where the attributes are + * field names. These are used to store auxiliary information about the document, such as its + * title, url, or an identifier to access a database. The set of stored fields are what is + * returned for each hit when searching. This is keyed by document number. + * <li>{@link org.apache.lucene.codecs.lucene101.Lucene101PostingsFormat Term dictionary}. A + * dictionary containing all of the terms used in all of the indexed fields of all of the + * documents. The dictionary also contains the number of documents which contain the term, and + * pointers to the term's frequency and proximity data. + * <li>{@link org.apache.lucene.codecs.lucene101.Lucene101PostingsFormat Term Frequency data}. For + * each term in the dictionary, the numbers of all the documents that contain that term, and + * the frequency of the term in that document, unless frequencies are omitted ({@link + * org.apache.lucene.index.IndexOptions#DOCS IndexOptions.DOCS}) + * <li>{@link org.apache.lucene.codecs.lucene101.Lucene101PostingsFormat Term Proximity data}. For + * each term in the dictionary, the positions that the term occurs in each document. Note that + * this will not exist if all fields in all documents omit position data. + * <li>{@link org.apache.lucene.codecs.lucene90.Lucene90NormsFormat Normalization factors}. For + * each field in each document, a value is stored that is multiplied into the score for hits + * on that field. + * <li>{@link org.apache.lucene.codecs.lucene90.Lucene90TermVectorsFormat Term Vectors}. For each + * field in each document, the term vector (sometimes called document vector) may be stored. A + * term vector consists of term text and term frequency. To add Term Vectors to your index see + * the {@link org.apache.lucene.document.Field Field} constructors + * <li>{@link org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat Per-document values}. Like + * stored values, these are also keyed by document number, but are generally intended to be + * loaded into main memory for fast access. Whereas stored values are generally intended for + * summary results from searches, per-document values are useful for things like scoring + * factors. + * <li>{@link org.apache.lucene.codecs.lucene90.Lucene90LiveDocsFormat Live documents}. An + * optional file indicating which documents are live. + * <li>{@link org.apache.lucene.codecs.lucene90.Lucene90PointsFormat Point values}. Optional pair + * of files, recording dimensionally indexed fields, to enable fast numeric range filtering + * and large numeric values like BigInteger and BigDecimal (1D) and geographic shape + * intersection (2D, 3D). + * <li>{@link org.apache.lucene.codecs.lucene99.Lucene99HnswVectorsFormat Vector values}. The + * vector format stores numeric vectors in a format optimized for random access and + * computation, supporting high-dimensional nearest-neighbor search. + * </ul> + * + * <p>Details on each of these are provided in their linked pages. </div> <a id="File_Naming"></a> + * + * <h3>File Naming</h3> + * + * <div> + * + * <p>All files belonging to a segment have the same name with varying extensions. The extensions + * correspond to the different file formats described below. When using the Compound File format + * (default for small segments) these files (except for the Segment info file, the Lock file, and + * Deleted documents file) are collapsed into a single .cfs file (see below for details) + * + * <p>Typically, all segments in an index are stored in a single directory, although this is not + * required. + * + * <p>File names are never re-used. That is, when any file is saved to the Directory it is given a + * never before used filename. This is achieved using a simple generations approach. For example, + * the first segments file is segments_1, then segments_2, etc. The generation is a sequential long + * integer represented in alpha-numeric (base 36) form. </div> <a id="file-names"></a> + * + * <h3>Summary of File Extensions</h3> + * + * <div> + * + * <p>The following table summarizes the names and extensions of the files in Lucene: + * + * <table class="padding4" style="border-spacing: 1px; border-collapse: separate"> + * <caption>lucene filenames by extension</caption> + * <tr> + * <th>Name</th> + * <th>Extension</th> + * <th>Brief Description</th> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.index.SegmentInfos Segments File}</td> + * <td>segments_N</td> + * <td>Stores information about a commit point</td> + * </tr> + * <tr> + * <td><a href="#Lock_File">Lock File</a></td> + * <td>write.lock</td> + * <td>The Write lock prevents multiple IndexWriters from writing to the same + * file.</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene99.Lucene99SegmentInfoFormat Segment Info}</td> + * <td>.si</td> + * <td>Stores metadata about a segment</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90CompoundFormat Compound File}</td> + * <td>.cfs, .cfe</td> + * <td>An optional "virtual" file consisting of all the other index files for + * systems that frequently run out of file handles.</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene94.Lucene94FieldInfosFormat Fields}</td> + * <td>.fnm</td> + * <td>Stores information about the fields</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat Field Index}</td> + * <td>.fdx</td> + * <td>Contains pointers to field data</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90StoredFieldsFormat Field Data}</td> + * <td>.fdt</td> + * <td>The stored fields for documents</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene101.Lucene101PostingsFormat Term Dictionary}</td> + * <td>.tim</td> + * <td>The term dictionary, stores term info</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene101.Lucene101PostingsFormat Term Index}</td> + * <td>.tip</td> + * <td>The index into the Term Dictionary</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene101.Lucene101PostingsFormat Frequencies}</td> + * <td>.doc</td> + * <td>Contains the list of docs which contain each term along with frequency</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene101.Lucene101PostingsFormat Positions}</td> + * <td>.pos</td> + * <td>Stores position information about where a term occurs in the index</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene101.Lucene101PostingsFormat Payloads}</td> + * <td>.pay</td> + * <td>Stores additional per-position metadata information such as character offsets and user payloads</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90NormsFormat Norms}</td> + * <td>.nvd, .nvm</td> + * <td>Encodes length and boost factors for docs and fields</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90DocValuesFormat Per-Document Values}</td> + * <td>.dvd, .dvm</td> + * <td>Encodes additional scoring factors or other per-document information.</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90TermVectorsFormat Term Vector Index}</td> + * <td>.tvx</td> + * <td>Stores offset into the document data file</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90TermVectorsFormat Term Vector Data}</td> + * <td>.tvd</td> + * <td>Contains term vector data.</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90LiveDocsFormat Live Documents}</td> + * <td>.liv</td> + * <td>Info about what documents are live</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene90.Lucene90PointsFormat Point values}</td> + * <td>.kdd, .kdi, .kdm</td> + * <td>Holds indexed points</td> + * </tr> + * <tr> + * <td>{@link org.apache.lucene.codecs.lucene99.Lucene99HnswVectorsFormat Vector values}</td> + * <td>.vec, .vem, .veq, vex</td> Review Comment: should we also add `veb` and `vemb` files to the list? -- This is an automated message from the Apache Git Service. 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