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Support "x IS NOT NULL" clauses as indexscan conditions. This turns out

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to be just a minor extension of the previous patch that made "x IS NULL"
indexable, because we can treat the IS NOT NULL condition as if it were
"x < NULL" or "x > NULL" (depending on the index's NULLS FIRST/LAST option),
just like IS NULL is treated like "x = NULL".  Aside from any possible
usefulness in its own right, this is an important improvement for
index-optimized MAX/MIN aggregates: it is now reliably possible to get
a column's min or max value cheaply, even when there are a lot of nulls
cluttering the interesting end of the index.
This commit is contained in:
Tom Lane
2010-01-01 21:53:49 +00:00
parent 15faca2596
commit 29c4ad9829
18 changed files with 295 additions and 120 deletions
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4
doc/src/sgml/catalogs.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.215 2009/12/29 20:11:42 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.216 2010/01/01 21:53:48 tgl Exp $ -->
<!--
Documentation of the system catalogs, directed toward PostgreSQL developers
-->
@ -466,7 +466,7 @@
<entry><structfield>amsearchnulls</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Does the access method support IS NULL searches?</entry>
<entry>Does the access method support IS NULL/NOT NULL searches?</entry>
</row>
<row>

5
doc/src/sgml/indexam.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.31 2009/07/29 20:56:17 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.32 2010/01/01 21:53:49 tgl Exp $ -->
<chapter id="indexam">
<title>Index Access Method Interface Definition</title>
@ -134,7 +134,8 @@
null values. An index access method that sets
<structfield>amindexnulls</structfield> may also set
<structfield>amsearchnulls</structfield>, indicating that it supports
<literal>IS NULL</> clauses as search conditions.
<literal>IS NULL</> and <literal>IS NOT NULL</> clauses as search
conditions.
</para>
</sect1>

11
doc/src/sgml/indices.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/indices.sgml,v 1.79 2009/08/07 20:54:31 alvherre Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/indices.sgml,v 1.80 2010/01/01 21:53:49 tgl Exp $ -->
<chapter id="indexes">
<title id="indexes-title">Indexes</title>
@ -147,8 +147,8 @@ CREATE INDEX test1_id_index ON test1 (id);
Constructs equivalent to combinations of these operators, such as
<literal>BETWEEN</> and <literal>IN</>, can also be implemented with
a B-tree index search. Also, an <literal>IS NULL</> condition on
an index column can be used with a B-tree index.
a B-tree index search. Also, an <literal>IS NULL</> or <literal>IS NOT
NULL</> condition on an index column can be used with a B-tree index.
</para>
<para>
@ -180,8 +180,7 @@ CREATE INDEX test1_id_index ON test1 (id);
Hash indexes can only handle simple equality comparisons.
The query planner will consider using a hash index whenever an
indexed column is involved in a comparison using the
<literal>=</literal> operator. (Hash indexes do not support
<literal>IS NULL</> searches.)
<literal>=</literal> operator.
The following command is used to create a hash index:
<synopsis>
CREATE INDEX <replaceable>name</replaceable> ON <replaceable>table</replaceable> USING hash (<replaceable>column</replaceable>);
@ -1025,7 +1024,7 @@ SELECT am.amname AS index_method,
real statistics, some default values are assumed, which are
almost certain to be inaccurate. Examining an application's
index usage without having run <command>ANALYZE</command> is
therefore a lost cause.
therefore a lost cause.
See <xref linkend="vacuum-for-statistics" endterm="vacuum-for-statistics-title">
and <xref linkend="autovacuum" endterm="autovacuum-title"> for more information.
</para>