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Multi-column GIN indexes. Teodor Sigaev

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Tom Lane
2008-07-11 21:06:29 +00:00
parent 2d6599f471
commit 27cb66fdfe
15 changed files with 465 additions and 182 deletions
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37
doc/src/sgml/indices.sgml
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@ -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>.)
@ -336,14 +336,21 @@ 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.
@ -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>

6
doc/src/sgml/ref/create_index.sgml
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@ -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