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Indexes with INCLUDE columns and their support in B-tree

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This patch introduces INCLUDE clause to index definition.  This clause
specifies a list of columns which will be included as a non-key part in
the index.  The INCLUDE columns exist solely to allow more queries to
benefit from index-only scans.  Also, such columns don't need to have
appropriate operator classes.  Expressions are not supported as INCLUDE
columns since they cannot be used in index-only scans.

Index access methods supporting INCLUDE are indicated by amcaninclude flag
in IndexAmRoutine.  For now, only B-tree indexes support INCLUDE clause.

In B-tree indexes INCLUDE columns are truncated from pivot index tuples
(tuples located in non-leaf pages and high keys).  Therefore, B-tree indexes
now might have variable number of attributes.  This patch also provides
generic facility to support that: pivot tuples contain number of their
attributes in t_tid.ip_posid.  Free 13th bit of t_info is used for indicating
that.  This facility will simplify further support of index suffix truncation.
The changes of above are backward-compatible, pg_upgrade doesn't need special
handling of B-tree indexes for that.

Bump catalog version

Author: Anastasia Lubennikova with contribition by Alexander Korotkov and me
Reviewed by: Peter Geoghegan, Tomas Vondra, Antonin Houska, Jeff Janes,
			 David Rowley, Alexander Korotkov
Discussion: https://www.postgresql.org/message-id/flat/56168952.4010101@postgrespro.ru
This commit is contained in:
Teodor Sigaev
2018-04-07 23:00:39 +03:00
parent 01bb85169a
commit 8224de4f42
89 changed files with 2112 additions and 467 deletions
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62
doc/src/sgml/ref/create_index.sgml
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@@ -23,6 +23,7 @@ PostgreSQL documentation
<synopsis>
CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] <replaceable class="parameter">name</replaceable> ] ON [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ USING <replaceable class="parameter">method</replaceable> ]
( { <replaceable class="parameter">column_name</replaceable> | ( <replaceable class="parameter">expression</replaceable> ) } [ COLLATE <replaceable class="parameter">collation</replaceable> ] [ <replaceable class="parameter">opclass</replaceable> ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] )
[ INCLUDE ( <replaceable class="parameter">column_name</replaceable> [, ...] ) ]
[ WITH ( <replaceable class="parameter">storage_parameter</replaceable> = <replaceable class="parameter">value</replaceable> [, ... ] ) ]
[ TABLESPACE <replaceable class="parameter">tablespace_name</replaceable> ]
[ WHERE <replaceable class="parameter">predicate</replaceable> ]
@@ -143,6 +144,56 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] <replaceable class=
</listitem>
</varlistentry>
<varlistentry>
<term><literal>INCLUDE</literal></term>
<listitem>
<para>
The optional <literal>INCLUDE</literal> clause specifies a
list of columns which will be included as a non-key part in the index.
Columns listed in this clause cannot also be present as index key columns.
The <literal>INCLUDE</literal> columns exist solely to
allow more queries to benefit from <firstterm>index-only scans</firstterm>
by including the values of the specified columns in the index. These values
would otherwise have to be obtained by reading the table's heap.
</para>
<para>
In <literal>UNIQUE</literal> indexes, uniqueness is only enforced
for key columns. Columns listed in the <literal>INCLUDE</literal>
clause have no effect on uniqueness enforcement. Other constraints
(<literal>PRIMARY KEY</literal> and <literal>EXCLUDE</literal>) work
the same way.
</para>
<para>
Columns listed in the <literal>INCLUDE</literal> clause don't need
appropriate operator classes; the clause can contain non-key index
columns whose data types don't have operator classes defined for
a given access method.
</para>
<para>
Expressions are not supported as included columns since they cannot be
used in index-only scans.
</para>
<para>
Currently, only the B-tree index access method supports this feature.
In B-tree indexes, the values of columns listed in the
<literal>INCLUDE</literal> clause are included in leaf tuples which
are linked to the heap tuples, but are not included into pivot tuples
used for tree navigation. Therefore, moving columns from the list of
key columns to the <literal>INCLUDE</literal> clause can slightly
reduce index size and improve the tree branching factor.
</para>
<para>
Indexes with columns listed in the <literal>INCLUDE</literal> clause
are also called <quote>covering indexes</quote>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">name</replaceable></term>
<listitem>
@@ -729,13 +780,22 @@ Indexes:
<title>Examples</title>
<para>
To create a B-tree index on the column <literal>title</literal> in
To create a unique B-tree index on the column <literal>title</literal> in
the table <literal>films</literal>:
<programlisting>
CREATE UNIQUE INDEX title_idx ON films (title);
</programlisting>
</para>
<para>
To create a unique B-tree index on the column <literal>title</literal>
and included columns <literal>director</literal> and <literal>rating</literal>
in the table <literal>films</literal>:
<programlisting>
CREATE UNIQUE INDEX title_idx ON films (title) INCLUDE (director, rating);
</programlisting>
</para>
<para>
To create an index on the expression <literal>lower(title)</literal>,
allowing efficient case-insensitive searches: