[PATCH] Add section headings to index types doc

Hi hackers,

Every time I have to look up what kinds of operations each index type is
suitable for, I get annoyed by the index types page being virtually
unskimmable due to not having headings for each index type.

Attached is a patch that adds <sect2> tags for each index type to make
it easier to see where the description of each one starts.

- ilmari
-- 
"The surreality of the universe tends towards a maximum" -- Skud's Law
"Never formulate a law or axiom that you're not prepared to live with
 the consequences of."                              -- Skud's Meta-Law

From 57d9550b9286e7f6298763bb51d45393aa2eab4e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dagfinn=20Ilmari=20Manns=C3=A5ker?= <ilmari@ilmari.org>
Date: Fri, 31 Jul 2020 10:20:48 +0100
Subject: [PATCH] Add section headers to index types doc

This makes it easier to compare the properties of different index
types at a glance.
---
 doc/src/sgml/indices.sgml | 460 ++++++++++++++++++++------------------
 1 file changed, 242 insertions(+), 218 deletions(-)

diff --git a/doc/src/sgml/indices.sgml b/doc/src/sgml/indices.sgml
index 28adaba72d..332d161547 100644
--- a/doc/src/sgml/indices.sgml
+++ b/doc/src/sgml/indices.sgml
@@ -122,244 +122,268 @@
    B-tree indexes, which fit the most common situations.
   </para>
 
-  <para>
-   <indexterm>
-    <primary>index</primary>
-    <secondary>B-tree</secondary>
-   </indexterm>
-   <indexterm>
-    <primary>B-tree</primary>
-    <see>index</see>
-   </indexterm>
-   B-trees can handle equality and range queries on data that can be sorted
-   into some ordering.
-   In particular, the <productname>PostgreSQL</productname> query planner
-   will consider using a B-tree index whenever an indexed column is
-   involved in a comparison using one of these operators:
+  <sect2 id="indexes-types-btree">
+   <title>B-tree</title>
 
-   <simplelist>
-    <member><literal><</literal></member>
-    <member><literal><=</literal></member>
-    <member><literal>=</literal></member>
-    <member><literal>>=</literal></member>
-    <member><literal>></literal></member>
-   </simplelist>
+   <para>
+    <indexterm>
+     <primary>index</primary>
+     <secondary>B-tree</secondary>
+    </indexterm>
+    <indexterm>
+     <primary>B-tree</primary>
+     <see>index</see>
+    </indexterm>
+    B-trees can handle equality and range queries on data that can be sorted
+    into some ordering.
+    In particular, the <productname>PostgreSQL</productname> query planner
+    will consider using a B-tree index whenever an indexed column is
+    involved in a comparison using one of these operators:
 
-   Constructs equivalent to combinations of these operators, such as
-   <literal>BETWEEN</literal> and <literal>IN</literal>, can also be implemented with
-   a B-tree index search.  Also, an <literal>IS NULL</literal> or <literal>IS NOT
-   NULL</literal> condition on an index column can be used with a B-tree index.
-  </para>
+    <simplelist>
+     <member><literal><</literal></member>
+     <member><literal><=</literal></member>
+     <member><literal>=</literal></member>
+     <member><literal>>=</literal></member>
+     <member><literal>></literal></member>
+    </simplelist>
 
-  <para>
-   The optimizer can also use a B-tree index for queries involving the
-   pattern matching operators <literal>LIKE</literal> and <literal>~</literal>
-   <emphasis>if</emphasis> the pattern is a constant and is anchored to
-   the beginning of the string — for example, <literal>col LIKE
-   'foo%'</literal> or <literal>col ~ '^foo'</literal>, but not
-   <literal>col LIKE '%bar'</literal>. However, if your database does not
-   use the C locale you will need to create the index with a special
-   operator class to support indexing of pattern-matching queries; see
-   <xref linkend="indexes-opclass"/> below. It is also possible to use
-   B-tree indexes for <literal>ILIKE</literal> and
-   <literal>~*</literal>, but only if the pattern starts with
-   non-alphabetic characters, i.e., characters that are not affected by
-   upper/lower case conversion.
-  </para>
+    Constructs equivalent to combinations of these operators, such as
+    <literal>BETWEEN</literal> and <literal>IN</literal>, can also be implemented with
+    a B-tree index search.  Also, an <literal>IS NULL</literal> or <literal>IS NOT
+    NULL</literal> condition on an index column can be used with a B-tree index.
+   </para>
 
-  <para>
-   B-tree indexes can also be used to retrieve data in sorted order.
-   This is not always faster than a simple scan and sort, but it is
-   often helpful.
-  </para>
+   <para>
+    The optimizer can also use a B-tree index for queries involving the
+    pattern matching operators <literal>LIKE</literal> and <literal>~</literal>
+    <emphasis>if</emphasis> the pattern is a constant and is anchored to
+    the beginning of the string — for example, <literal>col LIKE
+    'foo%'</literal> or <literal>col ~ '^foo'</literal>, but not
+    <literal>col LIKE '%bar'</literal>. However, if your database does not
+    use the C locale you will need to create the index with a special
+    operator class to support indexing of pattern-matching queries; see
+    <xref linkend="indexes-opclass"/> below. It is also possible to use
+    B-tree indexes for <literal>ILIKE</literal> and
+    <literal>~*</literal>, but only if the pattern starts with
+    non-alphabetic characters, i.e., characters that are not affected by
+    upper/lower case conversion.
+   </para>
 
-  <para>
-   <indexterm>
-    <primary>index</primary>
-    <secondary>hash</secondary>
-   </indexterm>
-   <indexterm>
-    <primary>hash</primary>
-    <see>index</see>
-   </indexterm>
-   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.
-   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>);
-</synopsis>
-  </para>
+   <para>
+    B-tree indexes can also be used to retrieve data in sorted order.
+    This is not always faster than a simple scan and sort, but it is
+    often helpful.
+   </para>
+  </sect2>
 
-  <para>
-   <indexterm>
-    <primary>index</primary>
-    <secondary>GiST</secondary>
-   </indexterm>
-   <indexterm>
-    <primary>GiST</primary>
-    <see>index</see>
-   </indexterm>
-   GiST indexes are not a single kind of index, but rather an infrastructure
-   within which many different indexing strategies can be implemented.
-   Accordingly, the particular operators with which a GiST index can be
-   used vary depending on the indexing strategy (the <firstterm>operator
-   class</firstterm>).  As an example, the standard distribution of
-   <productname>PostgreSQL</productname> includes GiST operator classes
-   for several two-dimensional geometric data types, which support indexed
-   queries using these operators:
+  <sect2 id="indexes-types-hash">
+   <title>Hash</title>
 
-   <simplelist>
-    <member><literal><<</literal></member>
-    <member><literal>&<</literal></member>
-    <member><literal>&></literal></member>
-    <member><literal>>></literal></member>
-    <member><literal><<|</literal></member>
-    <member><literal>&<|</literal></member>
-    <member><literal>|&></literal></member>
-    <member><literal>|>></literal></member>
-    <member><literal>@></literal></member>
-    <member><literal><@</literal></member>
-    <member><literal>~=</literal></member>
-    <member><literal>&&</literal></member>
-   </simplelist>
+   <para>
+    <indexterm>
+     <primary>index</primary>
+     <secondary>hash</secondary>
+    </indexterm>
+    <indexterm>
+     <primary>hash</primary>
+     <see>index</see>
+    </indexterm>
+    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.
+    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>);
+    </synopsis>
+   </para>
+  </sect2>
 
-   (See <xref linkend="functions-geometry"/> for the meaning of
-   these operators.)
-   The GiST operator classes included in the standard distribution are
-   documented in <xref linkend="gist-builtin-opclasses-table"/>.
-   Many other GiST operator
-   classes are available in the <literal>contrib</literal> collection or as separate
-   projects.  For more information see <xref linkend="gist"/>.
-  </para>
+  <sect2 id="indexes-type-gist">
+   <title>GiST</title>
 
-  <para>
-   GiST indexes are also capable of optimizing <quote>nearest-neighbor</quote>
-   searches, such as
-<programlisting><![CDATA[
-SELECT * FROM places ORDER BY location <-> point '(101,456)' LIMIT 10;
-]]>
-</programlisting>
-   which finds the ten places closest to a given target point.  The ability
-   to do this is again dependent on the particular operator class being used.
-   In <xref linkend="gist-builtin-opclasses-table"/>, operators that can be
-   used in this way are listed in the column <quote>Ordering Operators</quote>.
-  </para>
+   <para>
+    <indexterm>
+     <primary>index</primary>
+     <secondary>GiST</secondary>
+    </indexterm>
+    <indexterm>
+     <primary>GiST</primary>
+     <see>index</see>
+    </indexterm>
+    GiST indexes are not a single kind of index, but rather an infrastructure
+    within which many different indexing strategies can be implemented.
+    Accordingly, the particular operators with which a GiST index can be
+    used vary depending on the indexing strategy (the <firstterm>operator
+    class</firstterm>).  As an example, the standard distribution of
+    <productname>PostgreSQL</productname> includes GiST operator classes
+    for several two-dimensional geometric data types, which support indexed
+    queries using these operators:
 
-  <para>
-   <indexterm>
-    <primary>index</primary>
-    <secondary>SP-GiST</secondary>
-   </indexterm>
-   <indexterm>
-    <primary>SP-GiST</primary>
-    <see>index</see>
-   </indexterm>
-   SP-GiST indexes, like GiST indexes, offer an infrastructure that supports
-   various kinds of searches.  SP-GiST permits implementation of a wide range
-   of different non-balanced disk-based data structures, such as quadtrees,
-   k-d trees, and radix trees (tries).  As an example, the standard distribution of
-   <productname>PostgreSQL</productname> includes SP-GiST operator classes
-   for two-dimensional points, which support indexed
-   queries using these operators:
+    <simplelist>
+     <member><literal><<</literal></member>
+     <member><literal>&<</literal></member>
+     <member><literal>&></literal></member>
+     <member><literal>>></literal></member>
+     <member><literal><<|</literal></member>
+     <member><literal>&<|</literal></member>
+     <member><literal>|&></literal></member>
+     <member><literal>|>></literal></member>
+     <member><literal>@></literal></member>
+     <member><literal><@</literal></member>
+     <member><literal>~=</literal></member>
+     <member><literal>&&</literal></member>
+    </simplelist>
 
-   <simplelist>
-    <member><literal><<</literal></member>
-    <member><literal>>></literal></member>
-    <member><literal>~=</literal></member>
-    <member><literal><@</literal></member>
-    <member><literal><^</literal></member>
-    <member><literal>>^</literal></member>
-   </simplelist>
+    (See <xref linkend="functions-geometry"/> for the meaning of
+    these operators.)
+    The GiST operator classes included in the standard distribution are
+    documented in <xref linkend="gist-builtin-opclasses-table"/>.
+    Many other GiST operator
+    classes are available in the <literal>contrib</literal> collection or as separate
+    projects.  For more information see <xref linkend="gist"/>.
+   </para>
 
-   (See <xref linkend="functions-geometry"/> for the meaning of
-   these operators.)
-   The SP-GiST operator classes included in the standard distribution are
-   documented in <xref linkend="spgist-builtin-opclasses-table"/>.
-   For more information see <xref linkend="spgist"/>.
-  </para>
+   <para>
+    GiST indexes are also capable of optimizing <quote>nearest-neighbor</quote>
+    searches, such as
+    <programlisting><![CDATA[
+    SELECT * FROM places ORDER BY location <-> point '(101,456)' LIMIT 10;
+    ]]>
+    </programlisting>
+    which finds the ten places closest to a given target point.  The ability
+    to do this is again dependent on the particular operator class being used.
+    In <xref linkend="gist-builtin-opclasses-table"/>, operators that can be
+    used in this way are listed in the column <quote>Ordering Operators</quote>.
+   </para>
+  </sect2>
 
-  <para>
-   Like GiST, SP-GiST supports <quote>nearest-neighbor</quote> searches.
-   For SP-GiST operator classes that support distance ordering, the
-   corresponding operator is specified in the <quote>Ordering Operators</quote>
-   column in <xref linkend="spgist-builtin-opclasses-table"/>.
-  </para>
+  <sect2 id="indexes-type-spgist">
+   <title>SP-GiST</title>
 
-  <para>
-   <indexterm>
-    <primary>index</primary>
-    <secondary>GIN</secondary>
-   </indexterm>
-   <indexterm>
-    <primary>GIN</primary>
-    <see>index</see>
-   </indexterm>
-   GIN indexes are <quote>inverted indexes</quote> which are appropriate for
-   data values that contain multiple component values, such as arrays.  An
-   inverted index contains a separate entry for each component value, and
-   can efficiently handle queries that test for the presence of specific
-   component values.
-  </para>
+   <para>
+    <indexterm>
+     <primary>index</primary>
+     <secondary>SP-GiST</secondary>
+    </indexterm>
+    <indexterm>
+     <primary>SP-GiST</primary>
+     <see>index</see>
+    </indexterm>
+    SP-GiST indexes, like GiST indexes, offer an infrastructure that supports
+    various kinds of searches.  SP-GiST permits implementation of a wide range
+    of different non-balanced disk-based data structures, such as quadtrees,
+    k-d trees, and radix trees (tries).  As an example, the standard distribution of
+    <productname>PostgreSQL</productname> includes SP-GiST operator classes
+    for two-dimensional points, which support indexed
+    queries using these operators:
 
-  <para>
-   Like GiST and SP-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.
-   As an example, the standard distribution of
-   <productname>PostgreSQL</productname> includes a GIN operator class
-   for arrays, which supports indexed queries using these operators:
+    <simplelist>
+     <member><literal><<</literal></member>
+     <member><literal>>></literal></member>
+     <member><literal>~=</literal></member>
+     <member><literal><@</literal></member>
+     <member><literal><^</literal></member>
+     <member><literal>>^</literal></member>
+    </simplelist>
 
-   <simplelist>
-    <member><literal><@</literal></member>
-    <member><literal>@></literal></member>
-    <member><literal>=</literal></member>
-    <member><literal>&&</literal></member>
-   </simplelist>
+    (See <xref linkend="functions-geometry"/> for the meaning of
+    these operators.)
+    The SP-GiST operator classes included in the standard distribution are
+    documented in <xref linkend="spgist-builtin-opclasses-table"/>.
+    For more information see <xref linkend="spgist"/>.
+   </para>
 
-   (See <xref linkend="functions-array"/> for the meaning of
-   these operators.)
-   The GIN operator classes included in the standard distribution are
-   documented in <xref linkend="gin-builtin-opclasses-table"/>.
-   Many other GIN operator
-   classes are available in the <literal>contrib</literal> collection or as separate
-   projects.  For more information see <xref linkend="gin"/>.
-  </para>
+   <para>
+    Like GiST, SP-GiST supports <quote>nearest-neighbor</quote> searches.
+    For SP-GiST operator classes that support distance ordering, the
+    corresponding operator is specified in the <quote>Ordering Operators</quote>
+    column in <xref linkend="spgist-builtin-opclasses-table"/>.
+   </para>
+  </sect2>
 
-  <para>
-   <indexterm>
-    <primary>index</primary>
-    <secondary>BRIN</secondary>
-   </indexterm>
-   <indexterm>
-    <primary>BRIN</primary>
-    <see>index</see>
-   </indexterm>
-   BRIN indexes (a shorthand for Block Range INdexes) store summaries about
-   the values stored in consecutive physical block ranges of a table.
-   Like GiST, SP-GiST and GIN,
-   BRIN can support many different indexing strategies,
-   and the particular operators with which a BRIN index can be used
-   vary depending on the indexing strategy.
-   For data types that have a linear sort order, the indexed data
-   corresponds to the minimum and maximum values of the
-   values in the column for each block range.  This supports indexed queries
-   using these operators:
+  <sect2 id="indexes-types-gin">
+   <title>GIN</title>
 
-   <simplelist>
-    <member><literal><</literal></member>
-    <member><literal><=</literal></member>
-    <member><literal>=</literal></member>
-    <member><literal>>=</literal></member>
-    <member><literal>></literal></member>
-   </simplelist>
+   <para>
+    <indexterm>
+     <primary>index</primary>
+     <secondary>GIN</secondary>
+    </indexterm>
+    <indexterm>
+     <primary>GIN</primary>
+     <see>index</see>
+    </indexterm>
+    GIN indexes are <quote>inverted indexes</quote> which are appropriate for
+    data values that contain multiple component values, such as arrays.  An
+    inverted index contains a separate entry for each component value, and
+    can efficiently handle queries that test for the presence of specific
+    component values.
+   </para>
 
-   The BRIN operator classes included in the standard distribution are
-   documented in <xref linkend="brin-builtin-opclasses-table"/>.
-   For more information see <xref linkend="brin"/>.
-  </para>
+   <para>
+    Like GiST and SP-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.
+    As an example, the standard distribution of
+    <productname>PostgreSQL</productname> includes a GIN operator class
+    for arrays, which supports indexed queries using these operators:
+
+    <simplelist>
+     <member><literal><@</literal></member>
+     <member><literal>@></literal></member>
+     <member><literal>=</literal></member>
+     <member><literal>&&</literal></member>
+    </simplelist>
+
+    (See <xref linkend="functions-array"/> for the meaning of
+    these operators.)
+    The GIN operator classes included in the standard distribution are
+    documented in <xref linkend="gin-builtin-opclasses-table"/>.
+    Many other GIN operator
+    classes are available in the <literal>contrib</literal> collection or as separate
+    projects.  For more information see <xref linkend="gin"/>.
+   </para>
+  </sect2>
+
+  <sect2 id="indexes-types-brin">
+   <title>BRIN</title>
+
+   <para>
+    <indexterm>
+     <primary>index</primary>
+     <secondary>BRIN</secondary>
+    </indexterm>
+    <indexterm>
+     <primary>BRIN</primary>
+     <see>index</see>
+    </indexterm>
+    BRIN indexes (a shorthand for Block Range INdexes) store summaries about
+    the values stored in consecutive physical block ranges of a table.
+    Like GiST, SP-GiST and GIN,
+    BRIN can support many different indexing strategies,
+    and the particular operators with which a BRIN index can be used
+    vary depending on the indexing strategy.
+    For data types that have a linear sort order, the indexed data
+    corresponds to the minimum and maximum values of the
+    values in the column for each block range.  This supports indexed queries
+    using these operators:
+
+    <simplelist>
+     <member><literal><</literal></member>
+     <member><literal><=</literal></member>
+     <member><literal>=</literal></member>
+     <member><literal>>=</literal></member>
+     <member><literal>></literal></member>
+    </simplelist>
+
+    The BRIN operator classes included in the standard distribution are
+    documented in <xref linkend="brin-builtin-opclasses-table"/>.
+    For more information see <xref linkend="brin"/>.
+   </para>
+  </sect2>
  </sect1>
 
 
-- 
2.27.0