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Doc: Restructure B-Tree support routine docs.

Use a top-level "variablelist", with one item per B-Tree support
function.  This structure matches the structure used by various
"Extensibility" sections in other documentation chapters for other index
access methods.

An explicit list makes it much clearer where each item begins and ends.
This wasn't really a problem before now, but an upcoming patch that adds
deduplication to nbtree will need to have its own new B-Tree support
function.  Ease the burden of translators by tidying up btree.sgml ahead
of committing the deduplication patch.
This commit is contained in:
Peter Geoghegan
2020-02-12 14:08:34 -08:00
parent 0973f5602c
commit caba0910af

View File

@ -207,226 +207,256 @@
<para> <para>
As shown in <xref linkend="xindex-btree-support-table"/>, btree defines As shown in <xref linkend="xindex-btree-support-table"/>, btree defines
one required and two optional support functions. one required and two optional support functions. The three
user-defined methods are:
</para> </para>
<variablelist>
<varlistentry>
<term><function>order</function></term>
<listitem>
<para>
For each combination of data types that a btree operator family
provides comparison operators for, it must provide a comparison
support function, registered in
<structname>pg_amproc</structname> with support function number 1
and
<structfield>amproclefttype</structfield>/<structfield>amprocrighttype</structfield>
equal to the left and right data types for the comparison (i.e.,
the same data types that the matching operators are registered
with in <structname>pg_amop</structname>). The comparison
function must take two non-null values
<replaceable>A</replaceable> and <replaceable>B</replaceable> and
return an <type>int32</type> value that is
<literal>&lt;</literal> <literal>0</literal>,
<literal>0</literal>, or <literal>&gt;</literal>
<literal>0</literal> when <replaceable>A</replaceable>
<literal>&lt;</literal> <replaceable>B</replaceable>,
<replaceable>A</replaceable> <literal>=</literal>
<replaceable>B</replaceable>, or <replaceable>A</replaceable>
<literal>&gt;</literal> <replaceable>B</replaceable>,
respectively. A null result is disallowed: all values of the
data type must be comparable. See
<filename>src/backend/access/nbtree/nbtcompare.c</filename> for
examples.
</para>
<para> <para>
For each combination of data types that a btree operator family provides If the compared values are of a collatable data type, the
comparison operators for, it must provide a comparison support function, appropriate collation OID will be passed to the comparison
registered in <structname>pg_amproc</structname> with support function support function, using the standard
number 1 and <function>PG_GET_COLLATION()</function> mechanism.
<structfield>amproclefttype</structfield>/<structfield>amprocrighttype</structfield> </para>
equal to the left and right data types for the comparison (i.e., the </listitem>
same data types that the matching operators are registered with </varlistentry>
in <structname>pg_amop</structname>). <varlistentry>
The comparison function must take two non-null values <term><function>sortsupport</function></term>
<replaceable>A</replaceable> and <replaceable>B</replaceable> and <listitem>
return an <type>int32</type> value that <para>
is <literal>&lt;</literal> <literal>0</literal>, <literal>0</literal>, Optionally, a btree operator family may provide <firstterm>sort
or <literal>&gt;</literal> <literal>0</literal> support</firstterm> function(s), registered under support
when <replaceable>A</replaceable> <literal>&lt;</literal> function number 2. These functions allow implementing
<replaceable>B</replaceable>, <replaceable>A</replaceable> comparisons for sorting purposes in a more efficient way than
<literal>=</literal> <replaceable>B</replaceable>, naively calling the comparison support function. The APIs
or <replaceable>A</replaceable> <literal>&gt;</literal> involved in this are defined in
<replaceable>B</replaceable>, respectively. <filename>src/include/utils/sortsupport.h</filename>.
A null result is disallowed: all values of the data type must be comparable. </para>
See <filename>src/backend/access/nbtree/nbtcompare.c</filename> for </listitem>
examples. </varlistentry>
</para> <varlistentry>
<term><function>inrange</function></term>
<listitem>
<indexterm>
<primary>in_range support functions</primary>
</indexterm>
<para> <indexterm>
If the compared values are of a collatable data type, the appropriate <primary>support functions</primary>
collation OID will be passed to the comparison support function, using <secondary>in_range</secondary>
the standard <function>PG_GET_COLLATION()</function> mechanism. </indexterm>
</para> <para>
Optionally, a btree operator family may provide
<firstterm>in_range</firstterm> support function(s), registered
under support function number 3. These are not used during btree
index operations; rather, they extend the semantics of the
operator family so that it can support window clauses containing
the <literal>RANGE</literal> <replaceable>offset</replaceable>
<literal>PRECEDING</literal> and <literal>RANGE</literal>
<replaceable>offset</replaceable> <literal>FOLLOWING</literal>
frame bound types (see <xref
linkend="syntax-window-functions"/>). Fundamentally, the extra
information provided is how to add or subtract an
<replaceable>offset</replaceable> value in a way that is
compatible with the family's data ordering.
</para>
<para> <para>
Optionally, a btree operator family may provide <firstterm>sort An <function>in_range</function> function must have the signature
support</firstterm> function(s), registered under support function number
2. These functions allow implementing comparisons for sorting purposes
in a more efficient way than naively calling the comparison support
function. The APIs involved in this are defined in
<filename>src/include/utils/sortsupport.h</filename>.
</para>
<indexterm>
<primary>in_range support functions</primary>
</indexterm>
<indexterm>
<primary>support functions</primary>
<secondary>in_range</secondary>
</indexterm>
<para>
Optionally, a btree operator family may
provide <firstterm>in_range</firstterm> support function(s), registered
under support function number 3. These are not used during btree index
operations; rather, they extend the semantics of the operator family so
that it can support window clauses containing
the <literal>RANGE</literal> <replaceable>offset</replaceable>
<literal>PRECEDING</literal>
and <literal>RANGE</literal> <replaceable>offset</replaceable>
<literal>FOLLOWING</literal> frame bound types (see
<xref linkend="syntax-window-functions"/>). Fundamentally, the extra
information provided is how to add or subtract
an <replaceable>offset</replaceable> value in a way that is compatible
with the family's data ordering.
</para>
<para>
An <function>in_range</function> function must have the signature
<synopsis> <synopsis>
in_range(<replaceable>val</replaceable> type1, <replaceable>base</replaceable> type1, <replaceable>offset</replaceable> type2, <replaceable>sub</replaceable> bool, <replaceable>less</replaceable> bool) in_range(<replaceable>val</replaceable> type1, <replaceable>base</replaceable> type1, <replaceable>offset</replaceable> type2, <replaceable>sub</replaceable> bool, <replaceable>less</replaceable> bool)
returns bool returns bool
</synopsis> </synopsis>
<replaceable>val</replaceable> and <replaceable>base</replaceable> must be <replaceable>val</replaceable> and
of the same type, which is one of the types supported by the operator <replaceable>base</replaceable> must be of the same type, which
family (i.e., a type for which it provides an ordering). is one of the types supported by the operator family (i.e., a
However, <replaceable>offset</replaceable> could be of a different type, type for which it provides an ordering). However,
which might be one otherwise unsupported by the family. An example is <replaceable>offset</replaceable> could be of a different type,
that the built-in <literal>time_ops</literal> family provides which might be one otherwise unsupported by the family. An
an <function>in_range</function> function that example is that the built-in <literal>time_ops</literal> family
has <replaceable>offset</replaceable> of type <type>interval</type>. provides an <function>in_range</function> function that has
A family can provide <function>in_range</function> functions for any of <replaceable>offset</replaceable> of type <type>interval</type>.
its supported types and one or more <replaceable>offset</replaceable> A family can provide <function>in_range</function> functions for
types. Each <function>in_range</function> function should be entered any of its supported types and one or more
in <structname>pg_amproc</structname> <replaceable>offset</replaceable> types. Each
with <structfield>amproclefttype</structfield> equal to <type>type1</type> <function>in_range</function> function should be entered in
and <structfield>amprocrighttype</structfield> equal to <type>type2</type>. <structname>pg_amproc</structname> with
</para> <structfield>amproclefttype</structfield> equal to
<type>type1</type> and <structfield>amprocrighttype</structfield>
equal to <type>type2</type>.
</para>
<para>
The essential semantics of an <function>in_range</function> function
depend on the two Boolean flag parameters. It should add or
subtract <replaceable>base</replaceable>
and <replaceable>offset</replaceable>, then
compare <replaceable>val</replaceable> to the result, as follows:
<itemizedlist>
<listitem>
<para> <para>
if <literal>!</literal><replaceable>sub</replaceable> and The essential semantics of an <function>in_range</function>
<literal>!</literal><replaceable>less</replaceable>, function depend on the two Boolean flag parameters. It should
return <replaceable>val</replaceable> <literal>&gt;=</literal> add or subtract <replaceable>base</replaceable> and
(<replaceable>base</replaceable> <literal>+</literal> <replaceable>offset</replaceable>, then compare
<replaceable>offset</replaceable>) <replaceable>val</replaceable> to the result, as follows:
<itemizedlist>
<listitem>
<para>
if <literal>!</literal><replaceable>sub</replaceable> and
<literal>!</literal><replaceable>less</replaceable>, return
<replaceable>val</replaceable> <literal>&gt;=</literal>
(<replaceable>base</replaceable> <literal>+</literal>
<replaceable>offset</replaceable>)
</para>
</listitem>
<listitem>
<para>
if <literal>!</literal><replaceable>sub</replaceable> and
<replaceable>less</replaceable>, return
<replaceable>val</replaceable> <literal>&lt;=</literal>
(<replaceable>base</replaceable> <literal>+</literal>
<replaceable>offset</replaceable>)
</para>
</listitem>
<listitem>
<para>
if <replaceable>sub</replaceable> and
<literal>!</literal><replaceable>less</replaceable>, return
<replaceable>val</replaceable> <literal>&gt;=</literal>
(<replaceable>base</replaceable> <literal>-</literal>
<replaceable>offset</replaceable>)
</para>
</listitem>
<listitem>
<para>
if <replaceable>sub</replaceable> and
<replaceable>less</replaceable>, return
<replaceable>val</replaceable> <literal>&lt;=</literal>
(<replaceable>base</replaceable> <literal>-</literal>
<replaceable>offset</replaceable>)
</para>
</listitem>
</itemizedlist>
Before doing so, the function should check the sign of
<replaceable>offset</replaceable>: if it is less than zero, raise
error
<literal>ERRCODE_INVALID_PRECEDING_OR_FOLLOWING_SIZE</literal>
(22013) with error text like <quote>invalid preceding or
following size in window function</quote>. (This is required by
the SQL standard, although nonstandard operator families might
perhaps choose to ignore this restriction, since there seems to
be little semantic necessity for it.) This requirement is
delegated to the <function>in_range</function> function so that
the core code needn't understand what <quote>less than
zero</quote> means for a particular data type.
</para> </para>
</listitem>
<listitem>
<para>
if <literal>!</literal><replaceable>sub</replaceable>
and <replaceable>less</replaceable>,
return <replaceable>val</replaceable> <literal>&lt;=</literal>
(<replaceable>base</replaceable> <literal>+</literal>
<replaceable>offset</replaceable>)
</para>
</listitem>
<listitem>
<para>
if <replaceable>sub</replaceable>
and <literal>!</literal><replaceable>less</replaceable>,
return <replaceable>val</replaceable> <literal>&gt;=</literal>
(<replaceable>base</replaceable> <literal>-</literal>
<replaceable>offset</replaceable>)
</para>
</listitem>
<listitem>
<para>
if <replaceable>sub</replaceable> and <replaceable>less</replaceable>,
return <replaceable>val</replaceable> <literal>&lt;=</literal>
(<replaceable>base</replaceable> <literal>-</literal>
<replaceable>offset</replaceable>)
</para>
</listitem>
</itemizedlist>
Before doing so, the function should check the sign
of <replaceable>offset</replaceable>: if it is less than zero, raise
error <literal>ERRCODE_INVALID_PRECEDING_OR_FOLLOWING_SIZE</literal> (22013)
with error text like <quote>invalid preceding or following size in window
function</quote>. (This is required by the SQL standard, although
nonstandard operator families might perhaps choose to ignore this
restriction, since there seems to be little semantic necessity for it.)
This requirement is delegated to the <function>in_range</function>
function so that the core code needn't understand what <quote>less than
zero</quote> means for a particular data type.
</para>
<para> <para>
An additional expectation is that <function>in_range</function> functions An additional expectation is that <function>in_range</function>
should, if practical, avoid throwing an error functions should, if practical, avoid throwing an error if
if <replaceable>base</replaceable> <literal>+</literal> <replaceable>base</replaceable> <literal>+</literal>
<replaceable>offset</replaceable> <replaceable>offset</replaceable> or
or <replaceable>base</replaceable> <literal>-</literal> <replaceable>base</replaceable> <literal>-</literal>
<replaceable>offset</replaceable> would overflow. <replaceable>offset</replaceable> would overflow. The correct
The correct comparison result can be determined even if that value would comparison result can be determined even if that value would be
be out of the data type's range. Note that if the data type includes out of the data type's range. Note that if the data type
concepts such as <quote>infinity</quote> or <quote>NaN</quote>, extra care includes concepts such as <quote>infinity</quote> or
may be needed to ensure that <function>in_range</function>'s results agree <quote>NaN</quote>, extra care may be needed to ensure that
with the normal sort order of the operator family. <function>in_range</function>'s results agree with the normal
</para> sort order of the operator family.
</para>
<para>
The results of the <function>in_range</function> function must be
consistent with the sort ordering imposed by the operator family.
To be precise, given any fixed values of <replaceable>offset</replaceable>
and <replaceable>sub</replaceable>, then:
<itemizedlist>
<listitem>
<para> <para>
If <function>in_range</function> with <replaceable>less</replaceable> = The results of the <function>in_range</function> function must be
true is true for some <replaceable>val1</replaceable> consistent with the sort ordering imposed by the operator family.
and <replaceable>base</replaceable>, it must be true for To be precise, given any fixed values of
every <replaceable>val2</replaceable> <literal>&lt;=</literal> <replaceable>offset</replaceable> and
<replaceable>val1</replaceable> with the <replaceable>sub</replaceable>, then:
same <replaceable>base</replaceable>. <itemizedlist>
<listitem>
<para>
If <function>in_range</function> with
<replaceable>less</replaceable> = true is true for some
<replaceable>val1</replaceable> and
<replaceable>base</replaceable>, it must be true for every
<replaceable>val2</replaceable> <literal>&lt;=</literal>
<replaceable>val1</replaceable> with the same
<replaceable>base</replaceable>.
</para>
</listitem>
<listitem>
<para>
If <function>in_range</function> with
<replaceable>less</replaceable> = true is false for some
<replaceable>val1</replaceable> and
<replaceable>base</replaceable>, it must be false for every
<replaceable>val2</replaceable> <literal>&gt;=</literal>
<replaceable>val1</replaceable> with the same
<replaceable>base</replaceable>.
</para>
</listitem>
<listitem>
<para>
If <function>in_range</function> with
<replaceable>less</replaceable> = true is true for some
<replaceable>val</replaceable> and
<replaceable>base1</replaceable>, it must be true for every
<replaceable>base2</replaceable> <literal>&gt;=</literal>
<replaceable>base1</replaceable> with the same
<replaceable>val</replaceable>.
</para>
</listitem>
<listitem>
<para>
If <function>in_range</function> with
<replaceable>less</replaceable> = true is false for some
<replaceable>val</replaceable> and
<replaceable>base1</replaceable>, it must be false for every
<replaceable>base2</replaceable> <literal>&lt;=</literal>
<replaceable>base1</replaceable> with the same
<replaceable>val</replaceable>.
</para>
</listitem>
</itemizedlist>
Analogous statements with inverted conditions hold when
<replaceable>less</replaceable> = false.
</para> </para>
</listitem>
<listitem>
<para>
If <function>in_range</function> with <replaceable>less</replaceable> =
true is false for some <replaceable>val1</replaceable>
and <replaceable>base</replaceable>, it must be false for
every <replaceable>val2</replaceable> <literal>&gt;=</literal>
<replaceable>val1</replaceable> with the
same <replaceable>base</replaceable>.
</para>
</listitem>
<listitem>
<para>
If <function>in_range</function> with <replaceable>less</replaceable> =
true is true for some <replaceable>val</replaceable>
and <replaceable>base1</replaceable>, it must be true for
every <replaceable>base2</replaceable> <literal>&gt;=</literal>
<replaceable>base1</replaceable> with the
same <replaceable>val</replaceable>.
</para>
</listitem>
<listitem>
<para>
If <function>in_range</function> with <replaceable>less</replaceable> =
true is false for some <replaceable>val</replaceable>
and <replaceable>base1</replaceable>, it must be false for
every <replaceable>base2</replaceable> <literal>&lt;=</literal>
<replaceable>base1</replaceable> with the
same <replaceable>val</replaceable>.
</para>
</listitem>
</itemizedlist>
Analogous statements with inverted conditions hold
when <replaceable>less</replaceable> = false.
</para>
<para> <para>
If the type being ordered (<type>type1</type>) is collatable, If the type being ordered (<type>type1</type>) is collatable, the
the appropriate collation OID will be passed to appropriate collation OID will be passed to the
the <function>in_range</function> function, using the standard <function>in_range</function> function, using the standard
PG_GET_COLLATION() mechanism. PG_GET_COLLATION() mechanism.
</para> </para>
<para> <para>
<function>in_range</function> functions need not handle NULL inputs, and <function>in_range</function> functions need not handle NULL
typically will be marked strict. inputs, and typically will be marked strict.
</para> </para>
</listitem>
</varlistentry>
</variablelist>
</sect1> </sect1>