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diff --git a/doc/src/sgml/html/pgtrgm.html b/doc/src/sgml/html/pgtrgm.html new file mode 100644 index 0000000..5a18b80 --- /dev/null +++ b/doc/src/sgml/html/pgtrgm.html @@ -0,0 +1,428 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>F.35. pg_trgm — support for similarity of text using trigram matching</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="pgsurgery.html" title="F.34. pg_surgery — perform low-level surgery on relation data" /><link rel="next" href="pgvisibility.html" title="F.36. pg_visibility — visibility map information and utilities" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.35. pg_trgm — + support for similarity of text using trigram matching</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="pgsurgery.html" title="F.34. pg_surgery — perform low-level surgery on relation data">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules and Extensions">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules and Extensions</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="pgvisibility.html" title="F.36. pg_visibility — visibility map information and utilities">Next</a></td></tr></table><hr /></div><div class="sect1" id="PGTRGM"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.35. pg_trgm — + support for similarity of text using trigram matching <a href="#PGTRGM" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="pgtrgm.html#PGTRGM-CONCEPTS">F.35.1. Trigram (or Trigraph) Concepts</a></span></dt><dt><span class="sect2"><a href="pgtrgm.html#PGTRGM-FUNCS-OPS">F.35.2. Functions and Operators</a></span></dt><dt><span class="sect2"><a href="pgtrgm.html#PGTRGM-GUC">F.35.3. GUC Parameters</a></span></dt><dt><span class="sect2"><a href="pgtrgm.html#PGTRGM-INDEX">F.35.4. Index Support</a></span></dt><dt><span class="sect2"><a href="pgtrgm.html#PGTRGM-TEXT-SEARCH">F.35.5. Text Search Integration</a></span></dt><dt><span class="sect2"><a href="pgtrgm.html#PGTRGM-REFERENCES">F.35.6. References</a></span></dt><dt><span class="sect2"><a href="pgtrgm.html#PGTRGM-AUTHORS">F.35.7. Authors</a></span></dt></dl></div><a id="id-1.11.7.45.2" class="indexterm"></a><p> + The <code class="filename">pg_trgm</code> module provides functions and operators + for determining the similarity of + alphanumeric text based on trigram matching, as + well as index operator classes that support fast searching for similar + strings. + </p><p> + This module is considered <span class="quote">“<span class="quote">trusted</span>”</span>, that is, it can be + installed by non-superusers who have <code class="literal">CREATE</code> privilege + on the current database. + </p><div class="sect2" id="PGTRGM-CONCEPTS"><div class="titlepage"><div><div><h3 class="title">F.35.1. Trigram (or Trigraph) Concepts <a href="#PGTRGM-CONCEPTS" class="id_link">#</a></h3></div></div></div><p> + A trigram is a group of three consecutive characters taken + from a string. We can measure the similarity of two strings by + counting the number of trigrams they share. This simple idea + turns out to be very effective for measuring the similarity of + words in many natural languages. + </p><div class="note"><h3 class="title">Note</h3><p> + <code class="filename">pg_trgm</code> ignores non-word characters + (non-alphanumerics) when extracting trigrams from a string. + Each word is considered to have two spaces + prefixed and one space suffixed when determining the set + of trigrams contained in the string. + For example, the set of trigrams in the string + <span class="quote">“<span class="quote"><code class="literal">cat</code></span>”</span> is + <span class="quote">“<span class="quote"><code class="literal"> c</code></span>”</span>, + <span class="quote">“<span class="quote"><code class="literal"> ca</code></span>”</span>, + <span class="quote">“<span class="quote"><code class="literal">cat</code></span>”</span>, and + <span class="quote">“<span class="quote"><code class="literal">at </code></span>”</span>. + The set of trigrams in the string + <span class="quote">“<span class="quote"><code class="literal">foo|bar</code></span>”</span> is + <span class="quote">“<span class="quote"><code class="literal"> f</code></span>”</span>, + <span class="quote">“<span class="quote"><code class="literal"> fo</code></span>”</span>, + <span class="quote">“<span class="quote"><code class="literal">foo</code></span>”</span>, + <span class="quote">“<span class="quote"><code class="literal">oo </code></span>”</span>, + <span class="quote">“<span class="quote"><code class="literal"> b</code></span>”</span>, + <span class="quote">“<span class="quote"><code class="literal"> ba</code></span>”</span>, + <span class="quote">“<span class="quote"><code class="literal">bar</code></span>”</span>, and + <span class="quote">“<span class="quote"><code class="literal">ar </code></span>”</span>. + </p></div></div><div class="sect2" id="PGTRGM-FUNCS-OPS"><div class="titlepage"><div><div><h3 class="title">F.35.2. Functions and Operators <a href="#PGTRGM-FUNCS-OPS" class="id_link">#</a></h3></div></div></div><p> + The functions provided by the <code class="filename">pg_trgm</code> module + are shown in <a class="xref" href="pgtrgm.html#PGTRGM-FUNC-TABLE" title="Table F.26. pg_trgm Functions">Table F.26</a>, the operators + in <a class="xref" href="pgtrgm.html#PGTRGM-OP-TABLE" title="Table F.27. pg_trgm Operators">Table F.27</a>. + </p><div class="table" id="PGTRGM-FUNC-TABLE"><p class="title"><strong>Table F.26. <code class="filename">pg_trgm</code> Functions</strong></p><div class="table-contents"><table class="table" summary="pg_trgm Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature"> + Function + </p> + <p> + Description + </p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.11.7.45.6.3.2.2.1.1.1.1" class="indexterm"></a> + <code class="function">similarity</code> ( <code class="type">text</code>, <code class="type">text</code> ) + → <code class="returnvalue">real</code> + </p> + <p> + Returns a number that indicates how similar the two arguments are. + The range of the result is zero (indicating that the two strings are + completely dissimilar) to one (indicating that the two strings are + identical). + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.11.7.45.6.3.2.2.2.1.1.1" class="indexterm"></a> + <code class="function">show_trgm</code> ( <code class="type">text</code> ) + → <code class="returnvalue">text[]</code> + </p> + <p> + Returns an array of all the trigrams in the given string. + (In practice this is seldom useful except for debugging.) + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.11.7.45.6.3.2.2.3.1.1.1" class="indexterm"></a> + <code class="function">word_similarity</code> ( <code class="type">text</code>, <code class="type">text</code> ) + → <code class="returnvalue">real</code> + </p> + <p> + Returns a number that indicates the greatest similarity between + the set of trigrams in the first string and any continuous extent + of an ordered set of trigrams in the second string. For details, see + the explanation below. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.11.7.45.6.3.2.2.4.1.1.1" class="indexterm"></a> + <code class="function">strict_word_similarity</code> ( <code class="type">text</code>, <code class="type">text</code> ) + → <code class="returnvalue">real</code> + </p> + <p> + Same as <code class="function">word_similarity</code>, but forces + extent boundaries to match word boundaries. Since we don't have + cross-word trigrams, this function actually returns greatest similarity + between first string and any continuous extent of words of the second + string. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.11.7.45.6.3.2.2.5.1.1.1" class="indexterm"></a> + <code class="function">show_limit</code> () + → <code class="returnvalue">real</code> + </p> + <p> + Returns the current similarity threshold used by the <code class="literal">%</code> + operator. This sets the minimum similarity between + two words for them to be considered similar enough to + be misspellings of each other, for example. + (<span class="emphasis"><em>Deprecated</em></span>; instead use <code class="command">SHOW</code> + <code class="varname">pg_trgm.similarity_threshold</code>.) + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <a id="id-1.11.7.45.6.3.2.2.6.1.1.1" class="indexterm"></a> + <code class="function">set_limit</code> ( <code class="type">real</code> ) + → <code class="returnvalue">real</code> + </p> + <p> + Sets the current similarity threshold that is used by the <code class="literal">%</code> + operator. The threshold must be between 0 and 1 (default is 0.3). + Returns the same value passed in. + (<span class="emphasis"><em>Deprecated</em></span>; instead use <code class="command">SET</code> + <code class="varname">pg_trgm.similarity_threshold</code>.) + </p></td></tr></tbody></table></div></div><br class="table-break" /><p> + Consider the following example: + +</p><pre class="programlisting"> +# SELECT word_similarity('word', 'two words'); + word_similarity +----------------- + 0.8 +(1 row) +</pre><p> + + In the first string, the set of trigrams is + <code class="literal">{" w"," wo","wor","ord","rd "}</code>. + In the second string, the ordered set of trigrams is + <code class="literal">{" t"," tw","two","wo "," w"," wo","wor","ord","rds","ds "}</code>. + The most similar extent of an ordered set of trigrams in the second string + is <code class="literal">{" w"," wo","wor","ord"}</code>, and the similarity is + <code class="literal">0.8</code>. + </p><p> + This function returns a value that can be approximately understood as the + greatest similarity between the first string and any substring of the second + string. However, this function does not add padding to the boundaries of + the extent. Thus, the number of additional characters present in the + second string is not considered, except for the mismatched word boundaries. + </p><p> + At the same time, <code class="function">strict_word_similarity</code> + selects an extent of words in the second string. In the example above, + <code class="function">strict_word_similarity</code> would select the + extent of a single word <code class="literal">'words'</code>, whose set of trigrams is + <code class="literal">{" w"," wo","wor","ord","rds","ds "}</code>. + +</p><pre class="programlisting"> +# SELECT strict_word_similarity('word', 'two words'), similarity('word', 'words'); + strict_word_similarity | similarity +------------------------+------------ + 0.571429 | 0.571429 +(1 row) +</pre><p> + </p><p> + Thus, the <code class="function">strict_word_similarity</code> function + is useful for finding the similarity to whole words, while + <code class="function">word_similarity</code> is more suitable for + finding the similarity for parts of words. + </p><div class="table" id="PGTRGM-OP-TABLE"><p class="title"><strong>Table F.27. <code class="filename">pg_trgm</code> Operators</strong></p><div class="table-contents"><table class="table" summary="pg_trgm Operators" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature"> + Operator + </p> + <p> + Description + </p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature"> + <code class="type">text</code> <code class="literal">%</code> <code class="type">text</code> + → <code class="returnvalue">boolean</code> + </p> + <p> + Returns <code class="literal">true</code> if its arguments have a similarity + that is greater than the current similarity threshold set by + <code class="varname">pg_trgm.similarity_threshold</code>. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <code class="type">text</code> <code class="literal"><%</code> <code class="type">text</code> + → <code class="returnvalue">boolean</code> + </p> + <p> + Returns <code class="literal">true</code> if the similarity between the trigram + set in the first argument and a continuous extent of an ordered trigram + set in the second argument is greater than the current word similarity + threshold set by <code class="varname">pg_trgm.word_similarity_threshold</code> + parameter. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <code class="type">text</code> <code class="literal">%></code> <code class="type">text</code> + → <code class="returnvalue">boolean</code> + </p> + <p> + Commutator of the <code class="literal"><%</code> operator. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <code class="type">text</code> <code class="literal"><<%</code> <code class="type">text</code> + → <code class="returnvalue">boolean</code> + </p> + <p> + Returns <code class="literal">true</code> if its second argument has a continuous + extent of an ordered trigram set that matches word boundaries, + and its similarity to the trigram set of the first argument is greater + than the current strict word similarity threshold set by the + <code class="varname">pg_trgm.strict_word_similarity_threshold</code> parameter. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <code class="type">text</code> <code class="literal">%>></code> <code class="type">text</code> + → <code class="returnvalue">boolean</code> + </p> + <p> + Commutator of the <code class="literal"><<%</code> operator. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <code class="type">text</code> <code class="literal"><-></code> <code class="type">text</code> + → <code class="returnvalue">real</code> + </p> + <p> + Returns the <span class="quote">“<span class="quote">distance</span>”</span> between the arguments, that is + one minus the <code class="function">similarity()</code> value. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <code class="type">text</code> <code class="literal"><<-></code> <code class="type">text</code> + → <code class="returnvalue">real</code> + </p> + <p> + Returns the <span class="quote">“<span class="quote">distance</span>”</span> between the arguments, that is + one minus the <code class="function">word_similarity()</code> value. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <code class="type">text</code> <code class="literal"><->></code> <code class="type">text</code> + → <code class="returnvalue">real</code> + </p> + <p> + Commutator of the <code class="literal"><<-></code> operator. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <code class="type">text</code> <code class="literal"><<<-></code> <code class="type">text</code> + → <code class="returnvalue">real</code> + </p> + <p> + Returns the <span class="quote">“<span class="quote">distance</span>”</span> between the arguments, that is + one minus the <code class="function">strict_word_similarity()</code> value. + </p></td></tr><tr><td class="func_table_entry"><p class="func_signature"> + <code class="type">text</code> <code class="literal"><->>></code> <code class="type">text</code> + → <code class="returnvalue">real</code> + </p> + <p> + Commutator of the <code class="literal"><<<-></code> operator. + </p></td></tr></tbody></table></div></div><br class="table-break" /></div><div class="sect2" id="PGTRGM-GUC"><div class="titlepage"><div><div><h3 class="title">F.35.3. GUC Parameters <a href="#PGTRGM-GUC" class="id_link">#</a></h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt id="GUC-PGTRGM-SIMILARITY-THRESHOLD"><span class="term"> + <code class="varname">pg_trgm.similarity_threshold</code> (<code class="type">real</code>) + <a id="id-1.11.7.45.7.2.1.1.3" class="indexterm"></a> + </span> <a href="#GUC-PGTRGM-SIMILARITY-THRESHOLD" class="id_link">#</a></dt><dd><p> + Sets the current similarity threshold that is used by the <code class="literal">%</code> + operator. The threshold must be between 0 and 1 (default is 0.3). + </p></dd><dt id="GUC-PGTRGM-WORD-SIMILARITY-THRESHOLD"><span class="term"> + <code class="varname">pg_trgm.word_similarity_threshold</code> (<code class="type">real</code>) + <a id="id-1.11.7.45.7.2.2.1.3" class="indexterm"></a> + </span> <a href="#GUC-PGTRGM-WORD-SIMILARITY-THRESHOLD" class="id_link">#</a></dt><dd><p> + Sets the current word similarity threshold that is used by the + <code class="literal"><%</code> and <code class="literal">%></code> operators. The threshold + must be between 0 and 1 (default is 0.6). + </p></dd><dt id="GUC-PGTRGM-STRICT-WORD-SIMILARITY-THRESHOLD"><span class="term"> + <code class="varname">pg_trgm.strict_word_similarity_threshold</code> (<code class="type">real</code>) + <a id="id-1.11.7.45.7.2.3.1.3" class="indexterm"></a> + </span> <a href="#GUC-PGTRGM-STRICT-WORD-SIMILARITY-THRESHOLD" class="id_link">#</a></dt><dd><p> + Sets the current strict word similarity threshold that is used by the + <code class="literal"><<%</code> and <code class="literal">%>></code> operators. The threshold + must be between 0 and 1 (default is 0.5). + </p></dd></dl></div></div><div class="sect2" id="PGTRGM-INDEX"><div class="titlepage"><div><div><h3 class="title">F.35.4. Index Support <a href="#PGTRGM-INDEX" class="id_link">#</a></h3></div></div></div><p> + The <code class="filename">pg_trgm</code> module provides GiST and GIN index + operator classes that allow you to create an index over a text column for + the purpose of very fast similarity searches. These index types support + the above-described similarity operators, and additionally support + trigram-based index searches for <code class="literal">LIKE</code>, <code class="literal">ILIKE</code>, + <code class="literal">~</code>, <code class="literal">~*</code> and <code class="literal">=</code> queries. + The similarity comparisons are case-insensitive in a default build of + <code class="filename">pg_trgm</code>. + Inequality operators are not supported. + Note that those indexes may not be as efficient as regular B-tree indexes + for equality operator. + </p><p> + Example: + +</p><pre class="programlisting"> +CREATE TABLE test_trgm (t text); +CREATE INDEX trgm_idx ON test_trgm USING GIST (t gist_trgm_ops); +</pre><p> +or +</p><pre class="programlisting"> +CREATE INDEX trgm_idx ON test_trgm USING GIN (t gin_trgm_ops); +</pre><p> + </p><p> + <code class="literal">gist_trgm_ops</code> GiST opclass approximates a set of + trigrams as a bitmap signature. Its optional integer parameter + <code class="literal">siglen</code> determines the + signature length in bytes. The default length is 12 bytes. + Valid values of signature length are between 1 and 2024 bytes. Longer + signatures lead to a more precise search (scanning a smaller fraction of the index and + fewer heap pages), at the cost of a larger index. + </p><p> + Example of creating such an index with a signature length of 32 bytes: + </p><pre class="programlisting"> +CREATE INDEX trgm_idx ON test_trgm USING GIST (t gist_trgm_ops(siglen=32)); +</pre><p> + At this point, you will have an index on the <code class="structfield">t</code> column that + you can use for similarity searching. A typical query is +</p><pre class="programlisting"> +SELECT t, similarity(t, '<em class="replaceable"><code>word</code></em>') AS sml + FROM test_trgm + WHERE t % '<em class="replaceable"><code>word</code></em>' + ORDER BY sml DESC, t; +</pre><p> + This will return all values in the text column that are sufficiently + similar to <em class="replaceable"><code>word</code></em>, sorted from best match to worst. The + index will be used to make this a fast operation even over very large data + sets. + </p><p> + A variant of the above query is +</p><pre class="programlisting"> +SELECT t, t <-> '<em class="replaceable"><code>word</code></em>' AS dist + FROM test_trgm + ORDER BY dist LIMIT 10; +</pre><p> + This can be implemented quite efficiently by GiST indexes, but not + by GIN indexes. It will usually beat the first formulation when only + a small number of the closest matches is wanted. + </p><p> + Also you can use an index on the <code class="structfield">t</code> column for word + similarity or strict word similarity. Typical queries are: +</p><pre class="programlisting"> +SELECT t, word_similarity('<em class="replaceable"><code>word</code></em>', t) AS sml + FROM test_trgm + WHERE '<em class="replaceable"><code>word</code></em>' <% t + ORDER BY sml DESC, t; +</pre><p> + and +</p><pre class="programlisting"> +SELECT t, strict_word_similarity('<em class="replaceable"><code>word</code></em>', t) AS sml + FROM test_trgm + WHERE '<em class="replaceable"><code>word</code></em>' <<% t + ORDER BY sml DESC, t; +</pre><p> + This will return all values in the text column for which there is a + continuous extent in the corresponding ordered trigram set that is + sufficiently similar to the trigram set of <em class="replaceable"><code>word</code></em>, + sorted from best match to worst. The index will be used to make this + a fast operation even over very large data sets. + </p><p> + Possible variants of the above queries are: +</p><pre class="programlisting"> +SELECT t, '<em class="replaceable"><code>word</code></em>' <<-> t AS dist + FROM test_trgm + ORDER BY dist LIMIT 10; +</pre><p> + and +</p><pre class="programlisting"> +SELECT t, '<em class="replaceable"><code>word</code></em>' <<<-> t AS dist + FROM test_trgm + ORDER BY dist LIMIT 10; +</pre><p> + This can be implemented quite efficiently by GiST indexes, but not + by GIN indexes. + </p><p> + Beginning in <span class="productname">PostgreSQL</span> 9.1, these index types also support + index searches for <code class="literal">LIKE</code> and <code class="literal">ILIKE</code>, for example +</p><pre class="programlisting"> +SELECT * FROM test_trgm WHERE t LIKE '%foo%bar'; +</pre><p> + The index search works by extracting trigrams from the search string + and then looking these up in the index. The more trigrams in the search + string, the more effective the index search is. Unlike B-tree based + searches, the search string need not be left-anchored. + </p><p> + Beginning in <span class="productname">PostgreSQL</span> 9.3, these index types also support + index searches for regular-expression matches + (<code class="literal">~</code> and <code class="literal">~*</code> operators), for example +</p><pre class="programlisting"> +SELECT * FROM test_trgm WHERE t ~ '(foo|bar)'; +</pre><p> + The index search works by extracting trigrams from the regular expression + and then looking these up in the index. The more trigrams that can be + extracted from the regular expression, the more effective the index search + is. Unlike B-tree based searches, the search string need not be + left-anchored. + </p><p> + For both <code class="literal">LIKE</code> and regular-expression searches, keep in mind + that a pattern with no extractable trigrams will degenerate to a full-index + scan. + </p><p> + The choice between GiST and GIN indexing depends on the relative + performance characteristics of GiST and GIN, which are discussed elsewhere. + </p></div><div class="sect2" id="PGTRGM-TEXT-SEARCH"><div class="titlepage"><div><div><h3 class="title">F.35.5. Text Search Integration <a href="#PGTRGM-TEXT-SEARCH" class="id_link">#</a></h3></div></div></div><p> + Trigram matching is a very useful tool when used in conjunction + with a full text index. In particular it can help to recognize + misspelled input words that will not be matched directly by the + full text search mechanism. + </p><p> + The first step is to generate an auxiliary table containing all + the unique words in the documents: + +</p><pre class="programlisting"> +CREATE TABLE words AS SELECT word FROM + ts_stat('SELECT to_tsvector(''simple'', bodytext) FROM documents'); +</pre><p> + + where <code class="structname">documents</code> is a table that has a text field + <code class="structfield">bodytext</code> that we wish to search. The reason for using + the <code class="literal">simple</code> configuration with the <code class="function">to_tsvector</code> + function, instead of using a language-specific configuration, + is that we want a list of the original (unstemmed) words. + </p><p> + Next, create a trigram index on the word column: + +</p><pre class="programlisting"> +CREATE INDEX words_idx ON words USING GIN (word gin_trgm_ops); +</pre><p> + + Now, a <code class="command">SELECT</code> query similar to the previous example can + be used to suggest spellings for misspelled words in user search terms. + A useful extra test is to require that the selected words are also of + similar length to the misspelled word. + </p><div class="note"><h3 class="title">Note</h3><p> + Since the <code class="structname">words</code> table has been generated as a separate, + static table, it will need to be periodically regenerated so that + it remains reasonably up-to-date with the document collection. + Keeping it exactly current is usually unnecessary. + </p></div></div><div class="sect2" id="PGTRGM-REFERENCES"><div class="titlepage"><div><div><h3 class="title">F.35.6. References <a href="#PGTRGM-REFERENCES" class="id_link">#</a></h3></div></div></div><p> + GiST Development Site + <a class="ulink" href="http://www.sai.msu.su/~megera/postgres/gist/" target="_top">http://www.sai.msu.su/~megera/postgres/gist/</a> + </p><p> + Tsearch2 Development Site + <a class="ulink" href="http://www.sai.msu.su/~megera/postgres/gist/tsearch/V2/" target="_top">http://www.sai.msu.su/~megera/postgres/gist/tsearch/V2/</a> + </p></div><div class="sect2" id="PGTRGM-AUTHORS"><div class="titlepage"><div><div><h3 class="title">F.35.7. Authors <a href="#PGTRGM-AUTHORS" class="id_link">#</a></h3></div></div></div><p> + Oleg Bartunov <code class="email"><<a class="email" href="mailto:oleg@sai.msu.su">oleg@sai.msu.su</a>></code>, Moscow, Moscow University, Russia + </p><p> + Teodor Sigaev <code class="email"><<a class="email" href="mailto:teodor@sigaev.ru">teodor@sigaev.ru</a>></code>, Moscow, Delta-Soft Ltd.,Russia + </p><p> + Alexander Korotkov <code class="email"><<a class="email" href="mailto:a.korotkov@postgrespro.ru">a.korotkov@postgrespro.ru</a>></code>, Moscow, Postgres Professional, Russia + </p><p> + Documentation: Christopher Kings-Lynne + </p><p> + This module is sponsored by Delta-Soft Ltd., Moscow, Russia. + </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="pgsurgery.html" title="F.34. pg_surgery — perform low-level surgery on relation data">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="contrib.html" title="Appendix F. 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