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Diffstat (limited to 'doc/src/sgml/gist.sgml')
| -rw-r--r-- | doc/src/sgml/gist.sgml | 31 |
1 files changed, 14 insertions, 17 deletions
diff --git a/doc/src/sgml/gist.sgml b/doc/src/sgml/gist.sgml index ed4c689a728..56e72f69bea 100644 --- a/doc/src/sgml/gist.sgml +++ b/doc/src/sgml/gist.sgml @@ -1,25 +1,22 @@ <!-- -$PostgreSQL: pgsql/doc/src/sgml/gist.sgml,v 1.24 2005/11/04 23:14:00 petere Exp $ +$PostgreSQL: pgsql/doc/src/sgml/gist.sgml,v 1.25 2005/11/07 17:36:44 tgl Exp $ --> <chapter id="GiST"> <title>GiST Indexes</title> -<sect1 id="gist-intro"> - <title>Introduction</title> - - <para> <indexterm> <primary>index</primary> <secondary>GiST</secondary> </indexterm> - <indexterm> - <primary>GiST</primary> - <see>index</see> - </indexterm> + +<sect1 id="gist-intro"> + <title>Introduction</title> + + <para> <acronym>GiST</acronym> stands for Generalized Search Tree. It is a balanced, tree-structured access method, that acts as a base template in - which to implement arbitrary indexing schemes. B+-trees, R-trees and many + which to implement arbitrary indexing schemes. B-trees, R-trees and many other indexing schemes can be implemented in <acronym>GiST</acronym>. </para> @@ -60,17 +57,17 @@ $PostgreSQL: pgsql/doc/src/sgml/gist.sgml,v 1.24 2005/11/04 23:14:00 petere Exp <para> This extensibility should not be confused with the extensibility of the other standard search trees in terms of the data they can handle. For - example, <productname>PostgreSQL</productname> supports extensible B+-trees - and R-trees. That means that you can use - <productname>PostgreSQL</productname> to build a B+-tree or R-tree over any - data type you want. But B+-trees only support range predicates + example, <productname>PostgreSQL</productname> supports extensible B-trees + and hash indexes. That means that you can use + <productname>PostgreSQL</productname> to build a B-tree or hash over any + data type you want. But B-trees only support range predicates (<literal><</literal>, <literal>=</literal>, <literal>></literal>), - and R-trees only support n-D range queries (contains, contained, equals). + and hash indexes only support equality queries. </para> <para> So if you index, say, an image collection with a - <productname>PostgreSQL</productname> B+-tree, you can only issue queries + <productname>PostgreSQL</productname> B-tree, you can only issue queries such as <quote>is imagex equal to imagey</quote>, <quote>is imagex less than imagey</quote> and <quote>is imagex greater than imagey</quote>? Depending on how you define <quote>equals</quote>, <quote>less than</quote> @@ -84,7 +81,7 @@ $PostgreSQL: pgsql/doc/src/sgml/gist.sgml,v 1.24 2005/11/04 23:14:00 petere Exp All it takes to get a <acronym>GiST</acronym> access method up and running is to implement seven user-defined methods, which define the behavior of keys in the tree. Of course these methods have to be pretty fancy to - support fancy queries, but for all the standard queries (B+-trees, + support fancy queries, but for all the standard queries (B-trees, R-trees, etc.) they're relatively straightforward. In short, <acronym>GiST</acronym> combines extensibility along with generality, code reuse, and a clean interface. |