Multi-column GIN indexes. Teodor Sigaev

2 files changed, 25 insertions, 18 deletions

diff --git a/doc/src/sgml/indices.sgml b/doc/src/sgml/indices.sgml
index 3de05419226..2ab713c39be 100644
--- a/doc/src/sgml/indices.sgml
+++ b/doc/src/sgml/indices.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/indices.sgml,v 1.73 2008/05/27 00:13:08 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/indices.sgml,v 1.74 2008/07/11 21:06:28 tgl Exp $ -->
 
 <chapter id="indexes">
  <title id="indexes-title">Indexes</title>
@@ -198,7 +198,7 @@ CREATE INDEX <replaceable>name</replaceable> ON <replaceable>table</replaceable>
     after a database crash.
     For these reasons, hash index use is presently discouraged.
    </para>
-  </note>  
+  </note>
 
   <para>
    <indexterm>
@@ -250,9 +250,9 @@ CREATE INDEX <replaceable>name</replaceable> ON <replaceable>table</replaceable>
    </indexterm>
    GIN indexes are inverted indexes which can handle values that contain more
    than one key, arrays for example. Like GiST, GIN can support
-   many different user-defined indexing strategies and the particular 
-   operators with which a GIN index can be used vary depending on the 
-   indexing strategy.  
+   many different user-defined indexing strategies and the particular
+   operators with which a GIN index can be used vary depending on the
+   indexing strategy.
    As an example, the standard distribution of
    <productname>PostgreSQL</productname> includes GIN operator classes
    for one-dimensional arrays, which support indexed
@@ -306,7 +306,7 @@ CREATE INDEX test2_mm_idx ON test2 (major, minor);
   </para>
 
   <para>
-   Currently, only the B-tree and GiST index types support multicolumn
+   Currently, only the B-tree, GiST and GIN index types support multicolumn
    indexes.  Up to 32 columns can be specified.  (This limit can be
    altered when building <productname>PostgreSQL</productname>; see the
    file <filename>pg_config_manual.h</filename>.)
@@ -336,15 +336,22 @@ CREATE INDEX test2_mm_idx ON test2 (major, minor);
 
   <para>
    A multicolumn GiST index can be used with query conditions that
-   involve any subset of the index's columns. Conditions on additional 
-   columns restrict the entries returned by the index, but the condition on 
-   the first column is the most important one for determining how much of 
-   the index needs to be scanned.  A GiST index will be relatively 
-   ineffective if its first column has only a few distinct values, even if 
+   involve any subset of the index's columns. Conditions on additional
+   columns restrict the entries returned by the index, but the condition on
+   the first column is the most important one for determining how much of
+   the index needs to be scanned.  A GiST index will be relatively
+   ineffective if its first column has only a few distinct values, even if
    there are many distinct values in additional columns.
   </para>
 
   <para>
+   A multicolumn GIN index can be used with query conditions that
+   involve any subset of the index's columns. Unlike B-tree or GiST,
+   index search effectiveness is the same regardless of which index column(s)
+   the query conditions use.
+  </para>
+
+  <para>
    Of course, each column must be used with operators appropriate to the index
    type; clauses that involve other operators will not be considered.
   </para>
@@ -551,7 +558,7 @@ CREATE UNIQUE INDEX <replaceable>name</replaceable> ON <replaceable>table</repla
   <para>
    <productname>PostgreSQL</productname> automatically creates a unique
    index when a unique constraint or a primary key is defined for a table.
-   The index covers the columns that make up the primary key or unique 
+   The index covers the columns that make up the primary key or unique
    columns (a multicolumn index, if appropriate), and is the mechanism
    that enforces the constraint.
   </para>
@@ -798,9 +805,9 @@ SELECT * FROM orders WHERE order_nr = 3501;
    or the index will not be recognized to be usable. Matching takes
    place at query planning time, not at run time. As a result,
    parameterized query clauses will not work with a partial index. For
-   example a prepared query with a parameter might specify 
-   <quote>x &lt; ?</quote> which will never imply 
-   <quote>x &lt; 2</quote> for all possible values of the parameter. 
+   example a prepared query with a parameter might specify
+   <quote>x &lt; ?</quote> which will never imply
+   <quote>x &lt; 2</quote> for all possible values of the parameter.
   </para>
 
   <para>
diff --git a/doc/src/sgml/ref/create_index.sgml b/doc/src/sgml/ref/create_index.sgml
index 32b7bbebd99..030fa1bb004 100644
--- a/doc/src/sgml/ref/create_index.sgml
+++ b/doc/src/sgml/ref/create_index.sgml
@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/create_index.sgml,v 1.67 2008/03/16 23:57:51 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/create_index.sgml,v 1.68 2008/07/11 21:06:29 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -394,7 +394,7 @@ Indexes:
   </para>
 
   <para>
-   Currently, only the B-tree and GiST index methods support
+   Currently, only the B-tree, GiST and GIN index methods support
    multicolumn indexes. Up to 32 fields can be specified by default.
    (This limit can be altered when building
    <productname>PostgreSQL</productname>.)  Only B-tree currently
@@ -423,7 +423,7 @@ Indexes:
    the optional clauses <literal>ASC</>, <literal>DESC</>, <literal>NULLS
    FIRST</>, and/or <literal>NULLS LAST</> can be specified to reverse
    the normal sort direction of the index.  Since an ordered index can be
-   scanned either forward or backward, it is not normally useful to create a 
+   scanned either forward or backward, it is not normally useful to create a
    single-column <literal>DESC</> index &mdash; that sort ordering is already
    available with a regular index.  The value of these options is that
    multicolumn indexes can be created that match the sort ordering requested