| /* |
| * 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. |
| */ |
| |
| /** |
| * Code to maintain and access indices. |
| * <h2>Table Of Contents</h2> |
| * <ol> |
| * <li><a href="#index">Index APIs</a> |
| * <ul> |
| * <li><a href="#writer">IndexWriter</a></li> |
| * <li><a href="#reader">IndexReader</a></li> |
| * <li><a href="#segments">Segments and docids</a></li> |
| * </ul> |
| * </li> |
| * <li><a href="#field_types">Field types</a> |
| * <ul> |
| * <li><a href="#postings-desc">Postings</a></li> |
| * <li><a href="#stored-fields">Stored Fields</a></li> |
| * <li><a href="#docvalues">DocValues</a></li> |
| * <li><a href="#points">Points</a></li> |
| * </ul> |
| * </li> |
| * <li><a href="#postings">Postings APIs</a> |
| * <ul> |
| * <li><a href="#fields">Fields</a></li> |
| * <li><a href="#terms">Terms</a></li> |
| * <li><a href="#documents">Documents</a></li> |
| * <li><a href="#positions">Positions</a></li> |
| * </ul> |
| * </li> |
| * <li><a href="#stats">Index Statistics</a> |
| * <ul> |
| * <li><a href="#termstats">Term-level</a></li> |
| * <li><a href="#fieldstats">Field-level</a></li> |
| * <li><a href="#segmentstats">Segment-level</a></li> |
| * <li><a href="#documentstats">Document-level</a></li> |
| * </ul> |
| * </li> |
| * </ol> |
| * <a name="index"></a> |
| * <h2>Index APIs</h2> |
| |
| * <a name="writer"></a> |
| * <h3>IndexWriter</h3> |
| |
| * <p>{@link org.apache.lucene.index.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 |
| * {@link org.apache.lucene.store.Directory}, depending on the configuration in {@link |
| * org.apache.lucene.index.IndexWriterConfig}. A Directory is an abstraction that typically |
| * represents a local file-system directory (see various implementations of {@link |
| * org.apache.lucene.store.FSDirectory}), but it may also stand for some other storage, such as |
| * RAM.</p> |
| |
| * <a name="reader"></a> |
| * <h3>IndexReader</h3> |
| |
| * <p>{@link org.apache.lucene.index.IndexReader} is used to read data from the index, and supports |
| * searching. Many thread-safe readers may be {@link org.apache.lucene.index.DirectoryReader#open} |
| * 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 {@link |
| * org.apache.lucene.index.DirectoryReader#openIfChanged}) in order to incorporate writes that may |
| * occur after it is opened.</p> |
| |
| * <a name="segments"></a> |
| * <h3>Segments and docids</h3> |
| |
| * <p>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.</p> |
| |
| * <p>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 {@link org.apache.lucene.index.LeafReader}, |
| * which is a reader for a single segment, deal in per-segment docids.</p> |
| * |
| * <p>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.</p> |
| |
| * <a name="field_types"></a> |
| * <h2>Field Types</h2> |
| * |
| * <a name="postings-desc"></a> |
| * |
| * <p>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 {@link org.apache.lucene.index.Term} |
| * (roughly, a word or token), to (the ordered list of) {@link org.apache.lucene.document.Document}s |
| * containing that Term. Codecs may additionally record |
| * {@link org.apache.lucene.index.ImpactsEnum#getImpacts 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.</p> |
| * |
| * <a name="stored-fields"></a> |
| * <p>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 {@link org.apache.lucene.index.StoredFieldVisitor}.</p> |
| |
| * <a name="docvalues"></a> |
| * <p>{@link org.apache.lucene.index.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.</p> |
| |
| * <a name="points"></a> |
| * <p>{@link org.apache.lucene.index.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.</p> |
| |
| * <a name="postings"></a> |
| * <h2>Postings APIs</h2> |
| * <a name="fields"></a> |
| * <h3> |
| * Fields |
| * </h3> |
| * <p> |
| * {@link org.apache.lucene.index.Fields} is the initial entry point into the |
| * postings APIs, this can be obtained in several ways: |
| * <pre class="prettyprint"> |
| * // access indexed fields for an index segment |
| * Fields fields = reader.fields(); |
| * // access term vector fields for a specified document |
| * Fields fields = reader.getTermVectors(docid); |
| * </pre> |
| * Fields implements Java's Iterable interface, so it's easy to enumerate the |
| * list of fields: |
| * <pre class="prettyprint"> |
| * // enumerate list of fields |
| * for (String field : fields) { |
| * // access the terms for this field |
| * Terms terms = fields.terms(field); |
| * } |
| * </pre> |
| * <a name="terms"></a> |
| * <h3> |
| * Terms |
| * </h3> |
| * <p> |
| * {@link org.apache.lucene.index.Terms} represents the collection of terms |
| * within a field, exposes some metadata and <a href="#fieldstats">statistics</a>, |
| * and an API for enumeration. |
| * <pre class="prettyprint"> |
| * // 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()); |
| * } |
| * </pre> |
| * {@link org.apache.lucene.index.TermsEnum} provides an iterator over the list |
| * of terms within a field, some <a href="#termstats">statistics</a> about the term, |
| * and methods to access the term's <a href="#documents">documents</a> and |
| * <a href="#positions">positions</a>. |
| * <pre class="prettyprint"> |
| * // 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); |
| * } |
| * </pre> |
| * <a name="documents"></a> |
| * <h3> |
| * Documents |
| * </h3> |
| * <p> |
| * {@link org.apache.lucene.index.PostingsEnum} is an extension of |
| * {@link org.apache.lucene.search.DocIdSetIterator}that iterates over the list of |
| * documents for a term, along with the term frequency within that document. |
| * <pre class="prettyprint"> |
| * int docid; |
| * while ((docid = docsEnum.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) { |
| * System.out.println(docid); |
| * System.out.println(docsEnum.freq()); |
| * } |
| * </pre> |
| * <a name="positions"></a> |
| * <h3> |
| * Positions |
| * </h3> |
| * <p> |
| * 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 |
| * <pre class="prettyprint"> |
| * 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()); |
| * } |
| * } |
| * </pre> |
| * <a name="stats"></a> |
| * <h2>Index Statistics</h2> |
| * <a name="termstats"></a> |
| * <h3> |
| * Term statistics |
| * </h3> |
| * <ul> |
| * <li>{@link org.apache.lucene.index.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. |
| * <li>{@link org.apache.lucene.index.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. |
| * </ul> |
| * <a name="fieldstats"></a> |
| * <h3> |
| * Field statistics |
| * </h3> |
| * <ul> |
| * <li>{@link org.apache.lucene.index.Terms#size}: Returns the number of |
| * unique terms in the field. This statistic may be unavailable |
| * (returns <code>-1</code>) for some Terms implementations such as |
| * {@link org.apache.lucene.index.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. |
| * <li>{@link org.apache.lucene.index.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. |
| * <li>{@link org.apache.lucene.index.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 {@link org.apache.lucene.index.TermsEnum#docFreq} |
| * across all terms in the field, and like docFreq() it will also count postings |
| * that appear in deleted documents. |
| * <li>{@link org.apache.lucene.index.Terms#getSumTotalTermFreq}: Returns the number |
| * of tokens for the field. This can be thought of as the sum of |
| * {@link org.apache.lucene.index.TermsEnum#totalTermFreq} across all terms in the |
| * field, and like totalTermFreq() it will also count occurrences that appear in |
| * deleted documents. |
| * </ul> |
| * <a name="segmentstats"></a> |
| * <h3> |
| * Segment statistics |
| * </h3> |
| * <ul> |
| * <li>{@link org.apache.lucene.index.IndexReader#maxDoc}: Returns the number of |
| * documents (including deleted documents) in the index. |
| * <li>{@link org.apache.lucene.index.IndexReader#numDocs}: Returns the number |
| * of live documents (excluding deleted documents) in the index. |
| * <li>{@link org.apache.lucene.index.IndexReader#numDeletedDocs}: Returns the |
| * number of deleted documents in the index. |
| * <li>{@link org.apache.lucene.index.Fields#size}: Returns the number of indexed |
| * fields. |
| * </ul> |
| * <a name="documentstats"></a> |
| * <h3> |
| * Document statistics |
| * </h3> |
| * <p> |
| * Document statistics are available during the indexing process for an indexed field: typically |
| * a {@link org.apache.lucene.search.similarities.Similarity} implementation will store some |
| * of these values (possibly in a lossy way), into the normalization value for the document in |
| * its {@link org.apache.lucene.search.similarities.Similarity#computeNorm} method. |
| * <ul> |
| * <li>{@link org.apache.lucene.index.FieldInvertState#getLength}: Returns the number of |
| * tokens for this field in the document. Note that this is just the number |
| * of times that {@link org.apache.lucene.analysis.TokenStream#incrementToken} returned |
| * true, and is unrelated to the values in |
| * {@link org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute}. |
| * <li>{@link org.apache.lucene.index.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. |
| * <li>{@link org.apache.lucene.index.FieldInvertState#getPosition}: Returns the accumulated |
| * position value for this field in the document: computed from the values of |
| * {@link org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute} and including |
| * {@link org.apache.lucene.analysis.Analyzer#getPositionIncrementGap}s across multivalued |
| * fields. |
| * <li>{@link org.apache.lucene.index.FieldInvertState#getOffset}: Returns the total |
| * character offset value for this field in the document: computed from the values of |
| * {@link org.apache.lucene.analysis.tokenattributes.OffsetAttribute} returned by |
| * {@link org.apache.lucene.analysis.TokenStream#end}, and including |
| * {@link org.apache.lucene.analysis.Analyzer#getOffsetGap}s across multivalued |
| * fields. |
| * <li>{@link org.apache.lucene.index.FieldInvertState#getUniqueTermCount}: Returns the number |
| * of unique terms encountered for this field in the document. |
| * <li>{@link org.apache.lucene.index.FieldInvertState#getMaxTermFrequency}: Returns the maximum |
| * frequency across all unique terms encountered for this field in the document. |
| * </ul> |
| * <p> |
| * Additional user-supplied statistics can be added to the document as DocValues fields and |
| * accessed via {@link org.apache.lucene.index.LeafReader#getNumericDocValues}. |
| */ |
| package org.apache.lucene.index; |
