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| * The ASF licenses this file to You under the Apache License, Version 2.0 |
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| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
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| |
| /** |
| * Lucene 8.6 file format. |
| * |
| * <h2>Apache Lucene - Index File Formats</h2> |
| * <div> |
| * <ul> |
| * <li><a href="#Introduction">Introduction</a></li> |
| * <li><a href="#Definitions">Definitions</a> |
| * <ul> |
| * <li><a href="#Inverted_Indexing">Inverted Indexing</a></li> |
| * <li><a href="#Types_of_Fields">Types of Fields</a></li> |
| * <li><a href="#Segments">Segments</a></li> |
| * <li><a href="#Document_Numbers">Document Numbers</a></li> |
| * </ul> |
| * </li> |
| * <li><a href="#Overview">Index Structure Overview</a></li> |
| * <li><a href="#File_Naming">File Naming</a></li> |
| * <li><a href="#file-names">Summary of File Extensions</a> |
| * <ul> |
| * <li><a href="#Lock_File">Lock File</a></li> |
| * <li><a href="#History">History</a></li> |
| * <li><a href="#Limitations">Limitations</a></li> |
| * </ul> |
| * </li> |
| * </ul> |
| * </div> |
| * <a name="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> |
| * <p>This document attempts to provide a high-level definition of the Apache |
| * Lucene file formats.</p> |
| * </div> |
| * <a name="Definitions"></a> |
| * <h3>Definitions</h3> |
| * <div> |
| * <p>The fundamental concepts in Lucene are index, document, field and term.</p> |
| * <p>An index contains a sequence of documents.</p> |
| * <ul> |
| * <li>A document is a sequence of fields.</li> |
| * <li>A field is a named sequence of terms.</li> |
| * <li>A term is a sequence of bytes.</li> |
| * </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.</p> |
| * <a name="Inverted_Indexing"></a> |
| * <h4>Inverted Indexing</h4> |
| * <p>The index stores statistics about terms in order to make term-based search |
| * more efficient. Lucene's 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.</p> |
| * <a name="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> |
| * <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> |
| * <p>See the {@link org.apache.lucene.document.Field Field} |
| * java docs for more information on Fields.</p> |
| * <a name="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:</p> |
| * <ol> |
| * <li>Creating new segments for newly added documents.</li> |
| * <li>Merging existing segments.</li> |
| * </ol> |
| * <p>Searches may involve multiple segments and/or multiple indexes, each index |
| * potentially composed of a set of segments.</p> |
| * <a name="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> |
| * <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:</p> |
| * <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.</p> |
| * </li> |
| * <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.</p> |
| * </li> |
| * </ul> |
| * </div> |
| * <a name="Overview"></a> |
| * <h3>Index Structure Overview</h3> |
| * <div> |
| * <p>Each segment index maintains the following:</p> |
| * <ul> |
| * <li> |
| * {@link org.apache.lucene.codecs.lucene86.Lucene86SegmentInfoFormat 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> |
| * <li> |
| * {@link org.apache.lucene.codecs.lucene60.Lucene60FieldInfosFormat Field names}. |
| * This contains the set of field names used in the index. |
| * </li> |
| * <li> |
| * 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> |
| * <li> |
| * {@link org.apache.lucene.codecs.lucene84.Lucene84PostingsFormat 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> |
| * <li> |
| * {@link org.apache.lucene.codecs.lucene84.Lucene84PostingsFormat 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> |
| * <li> |
| * {@link org.apache.lucene.codecs.lucene84.Lucene84PostingsFormat 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> |
| * <li> |
| * {@link org.apache.lucene.codecs.lucene80.Lucene80NormsFormat Normalization factors}. |
| * For each field in each document, a value is stored |
| * that is multiplied into the score for hits on that field. |
| * </li> |
| * <li> |
| * {@link org.apache.lucene.codecs.lucene50.Lucene50TermVectorsFormat 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> |
| * <li> |
| * {@link org.apache.lucene.codecs.lucene80.Lucene80DocValuesFormat 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> |
| * <li> |
| * {@link org.apache.lucene.codecs.lucene50.Lucene50LiveDocsFormat Live documents}. |
| * An optional file indicating which documents are live. |
| * </li> |
| * <li> |
| * {@link org.apache.lucene.codecs.lucene86.Lucene86PointsFormat 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> |
| * </ul> |
| * <p>Details on each of these are provided in their linked pages.</p> |
| * </div> |
| * <a name="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> |
| * <p>Typically, all segments in an index are stored in a single directory, |
| * although this is not required.</p> |
| * <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.</p> |
| * </div> |
| * <a name="file-names"></a> |
| * <h3>Summary of File Extensions</h3> |
| * <div> |
| * <p>The following table summarizes the names and extensions of the files in |
| * Lucene:</p> |
| * <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.lucene86.Lucene86SegmentInfoFormat Segment Info}</td> |
| * <td>.si</td> |
| * <td>Stores metadata about a segment</td> |
| * </tr> |
| * <tr> |
| * <td>{@link org.apache.lucene.codecs.lucene50.Lucene50CompoundFormat 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.lucene60.Lucene60FieldInfosFormat Fields}</td> |
| * <td>.fnm</td> |
| * <td>Stores information about the fields</td> |
| * </tr> |
| * <tr> |
| * <td>Field Index</td> |
| * <td>.fdx</td> |
| * <td>Contains pointers to field data</td> |
| * </tr> |
| * <tr> |
| * <td>Field Data</td> |
| * <td>.fdt</td> |
| * <td>The stored fields for documents</td> |
| * </tr> |
| * <tr> |
| * <td>{@link org.apache.lucene.codecs.lucene84.Lucene84PostingsFormat Term Dictionary}</td> |
| * <td>.tim</td> |
| * <td>The term dictionary, stores term info</td> |
| * </tr> |
| * <tr> |
| * <td>{@link org.apache.lucene.codecs.lucene84.Lucene84PostingsFormat Term Index}</td> |
| * <td>.tip</td> |
| * <td>The index into the Term Dictionary</td> |
| * </tr> |
| * <tr> |
| * <td>{@link org.apache.lucene.codecs.lucene84.Lucene84PostingsFormat 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.lucene84.Lucene84PostingsFormat 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.lucene84.Lucene84PostingsFormat 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.lucene80.Lucene80NormsFormat 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.lucene80.Lucene80DocValuesFormat 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.lucene50.Lucene50TermVectorsFormat Term Vector Index}</td> |
| * <td>.tvx</td> |
| * <td>Stores offset into the document data file</td> |
| * </tr> |
| * <tr> |
| * <td>{@link org.apache.lucene.codecs.lucene50.Lucene50TermVectorsFormat Term Vector Data}</td> |
| * <td>.tvd</td> |
| * <td>Contains term vector data.</td> |
| * </tr> |
| * <tr> |
| * <td>{@link org.apache.lucene.codecs.lucene50.Lucene50LiveDocsFormat Live Documents}</td> |
| * <td>.liv</td> |
| * <td>Info about what documents are live</td> |
| * </tr> |
| * <tr> |
| * <td>{@link org.apache.lucene.codecs.lucene86.Lucene86PointsFormat Point values}</td> |
| * <td>.dii, .dim</td> |
| * <td>Holds indexed points, if any</td> |
| * </tr> |
| * </table> |
| * </div> |
| * <a name="Lock_File"></a> |
| * <h3>Lock File</h3> |
| * The write lock, which is stored in the index directory by default, is named |
| * "write.lock". If the lock directory is different from the index directory then |
| * the write lock will be named "XXXX-write.lock" where XXXX is a unique prefix |
| * derived from the full path to the index directory. When this file is present, a |
| * writer is currently modifying the index (adding or removing documents). This |
| * lock file ensures that only one writer is modifying the index at a time. |
| * <a name="History"></a> |
| * <h3>History</h3> |
| * <p>Compatibility notes are provided in this document, describing how file |
| * formats have changed from prior versions:</p> |
| * <ul> |
| * <li>In version 2.1, the file format was changed to allow lock-less commits (ie, |
| * no more commit lock). The change is fully backwards compatible: you can open a |
| * pre-2.1 index for searching or adding/deleting of docs. When the new segments |
| * file is saved (committed), it will be written in the new file format (meaning |
| * no specific "upgrade" process is needed). But note that once a commit has |
| * occurred, pre-2.1 Lucene will not be able to read the index.</li> |
| * <li>In version 2.3, the file format was changed to allow segments to share a |
| * single set of doc store (vectors & stored fields) files. This allows for |
| * faster indexing in certain cases. The change is fully backwards compatible (in |
| * the same way as the lock-less commits change in 2.1).</li> |
| * <li>In version 2.4, Strings are now written as true UTF-8 byte sequence, not |
| * Java's modified UTF-8. See <a href="http://issues.apache.org/jira/browse/LUCENE-510"> |
| * LUCENE-510</a> for details.</li> |
| * <li>In version 2.9, an optional opaque Map<String,String> CommitUserData |
| * may be passed to IndexWriter's commit methods (and later retrieved), which is |
| * recorded in the segments_N file. See <a href="http://issues.apache.org/jira/browse/LUCENE-1382"> |
| * LUCENE-1382</a> for details. Also, |
| * diagnostics were added to each segment written recording details about why it |
| * was written (due to flush, merge; which OS/JRE was used; etc.). See issue |
| * <a href="http://issues.apache.org/jira/browse/LUCENE-1654">LUCENE-1654</a> for details.</li> |
| * <li>In version 3.0, compressed fields are no longer written to the index (they |
| * can still be read, but on merge the new segment will write them, uncompressed). |
| * See issue <a href="http://issues.apache.org/jira/browse/LUCENE-1960">LUCENE-1960</a> |
| * for details.</li> |
| * <li>In version 3.1, segments records the code version that created them. See |
| * <a href="http://issues.apache.org/jira/browse/LUCENE-2720">LUCENE-2720</a> for details. |
| * Additionally segments track explicitly whether or not they have term vectors. |
| * See <a href="http://issues.apache.org/jira/browse/LUCENE-2811">LUCENE-2811</a> |
| * for details.</li> |
| * <li>In version 3.2, numeric fields are written as natively to stored fields |
| * file, previously they were stored in text format only.</li> |
| * <li>In version 3.4, fields can omit position data while still indexing term |
| * frequencies.</li> |
| * <li>In version 4.0, the format of the inverted index became extensible via |
| * the {@link org.apache.lucene.codecs.Codec Codec} api. Fast per-document storage |
| * ({@code DocValues}) was introduced. Normalization factors need no longer be a |
| * single byte, they can be any {@link org.apache.lucene.index.NumericDocValues NumericDocValues}. |
| * Terms need not be unicode strings, they can be any byte sequence. Term offsets |
| * can optionally be indexed into the postings lists. Payloads can be stored in the |
| * term vectors.</li> |
| * <li>In version 4.1, the format of the postings list changed to use either |
| * of FOR compression or variable-byte encoding, depending upon the frequency |
| * of the term. Terms appearing only once were changed to inline directly into |
| * the term dictionary. Stored fields are compressed by default. </li> |
| * <li>In version 4.2, term vectors are compressed by default. DocValues has |
| * a new multi-valued type (SortedSet), that can be used for faceting/grouping/joining |
| * on multi-valued fields.</li> |
| * <li>In version 4.5, DocValues were extended to explicitly represent missing values.</li> |
| * <li>In version 4.6, FieldInfos were extended to support per-field DocValues generation, to |
| * allow updating NumericDocValues fields.</li> |
| * <li>In version 4.8, checksum footers were added to the end of each index file |
| * for improved data integrity. Specifically, the last 8 bytes of every index file |
| * contain the zlib-crc32 checksum of the file.</li> |
| * <li>In version 4.9, DocValues has a new multi-valued numeric type (SortedNumeric) |
| * that is suitable for faceting/sorting/analytics. |
| * <li>In version 5.4, DocValues have been improved to store more information on disk: |
| * addresses for binary fields and ord indexes for multi-valued fields. |
| * <li>In version 6.0, Points were added, for multi-dimensional range/distance search. |
| * <li>In version 6.2, new Segment info format that reads/writes the index sort, to support index sorting. |
| * <li>In version 7.0, DocValues have been improved to better support sparse doc values |
| * thanks to an iterator API.</li> |
| * <li>In version 8.0, postings have been enhanced to record, for each block of |
| * doc ids, the (term freq, normalization factor) pairs that may trigger the |
| * maximum score of the block. This information is recorded alongside skip data |
| * in order to be able to skip blocks of doc ids if they may not produce high |
| * enough scores. |
| * Additionally doc values and norms has been extended with jump-tables to make access O(1) |
| * instead of O(n), where n is the number of elements to skip when advancing in the data.</li> |
| * <li>In version 8.4, postings, positions, offsets and payload lengths have move to a more |
| * performant encoding that is vectorized.</li> |
| * <li>In version 8.6, index sort serialization is delegated to the sorts themselves, to |
| * allow user-defined sorts to be used</li> |
| * </ul> |
| * <a name="Limitations"></a> |
| * <h3>Limitations</h3> |
| * <div> |
| * <p>Lucene uses a Java <code>int</code> to refer to |
| * document numbers, and the index file format uses an <code>Int32</code> |
| * on-disk to store document numbers. This is a limitation |
| * of both the index file format and the current implementation. Eventually these |
| * should be replaced with either <code>UInt64</code> values, or |
| * better yet, {@link org.apache.lucene.store.DataOutput#writeVInt VInt} values which have no limit.</p> |
| * </div> |
| */ |
| package org.apache.lucene.codecs.lucene86; |
