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Postgres FD Implementation
Commit caba0910 authored by Peter Geoghegan's avatar Peter Geoghegan
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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.
parent 0973f560
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doc/src/sgml/btree.sgml
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......@@ -207,48 +207,64 @@
<para>
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>
<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
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
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
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>
If the compared values are of a collatable data type, the appropriate
collation OID will be passed to the comparison support function, using
the standard <function>PG_GET_COLLATION()</function> mechanism.
If the compared values are of a collatable data type, the
appropriate collation OID will be passed to the comparison
support function, using the standard
<function>PG_GET_COLLATION()</function> mechanism.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><function>sortsupport</function></term>
<listitem>
<para>
Optionally, a btree operator family may provide <firstterm>sort
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
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>
</listitem>
</varlistentry>
<varlistentry>
<term><function>inrange</function></term>
<listitem>
<indexterm>
<primary>in_range support functions</primary>
</indexterm>
......@@ -257,21 +273,20 @@
<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
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.
<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>
......@@ -280,153 +295,168 @@
in_range(<replaceable>val</replaceable> type1, <replaceable>base</replaceable> type1, <replaceable>offset</replaceable> type2, <replaceable>sub</replaceable> bool, <replaceable>less</replaceable> bool)
returns bool
</synopsis>
<replaceable>val</replaceable> and <replaceable>base</replaceable> must be
of the same type, which is one of the types supported by the operator
family (i.e., a type for which it provides an ordering).
However, <replaceable>offset</replaceable> could be of a different type,
which might be one otherwise unsupported by the family. An example is
that the built-in <literal>time_ops</literal> family provides
an <function>in_range</function> function that
has <replaceable>offset</replaceable> of type <type>interval</type>.
A family can provide <function>in_range</function> functions for any of
its supported types and one or more <replaceable>offset</replaceable>
types. Each <function>in_range</function> function should be entered
in <structname>pg_amproc</structname>
with <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:
<replaceable>val</replaceable> and
<replaceable>base</replaceable> must be of the same type, which
is one of the types supported by the operator family (i.e., a
type for which it provides an ordering). However,
<replaceable>offset</replaceable> could be of a different type,
which might be one otherwise unsupported by the family. An
example is that the built-in <literal>time_ops</literal> family
provides an <function>in_range</function> function that has
<replaceable>offset</replaceable> of type <type>interval</type>.
A family can provide <function>in_range</function> functions for
any of its supported types and one or more
<replaceable>offset</replaceable> types. Each
<function>in_range</function> function should be entered in
<structname>pg_amproc</structname> with
<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>
if <literal>!</literal><replaceable>sub</replaceable> and
<literal>!</literal><replaceable>less</replaceable>,
return <replaceable>val</replaceable> <literal>&gt;=</literal>
<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>
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>
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>
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
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>
An additional expectation is that <function>in_range</function> functions
should, if practical, avoid throwing an error
if <replaceable>base</replaceable> <literal>+</literal>
<replaceable>offset</replaceable>
or <replaceable>base</replaceable> <literal>-</literal>
<replaceable>offset</replaceable> would overflow.
The correct comparison result can be determined even if that value would
be out of the data type's range. Note that if the data type includes
concepts such as <quote>infinity</quote> or <quote>NaN</quote>, extra care
may be needed to ensure that <function>in_range</function>'s results agree
with the normal sort order of the operator family.
An additional expectation is that <function>in_range</function>
functions should, if practical, avoid throwing an error if
<replaceable>base</replaceable> <literal>+</literal>
<replaceable>offset</replaceable> or
<replaceable>base</replaceable> <literal>-</literal>
<replaceable>offset</replaceable> would overflow. The correct
comparison result can be determined even if that value would be
out of the data type's range. Note that if the data type
includes concepts such as <quote>infinity</quote> or
<quote>NaN</quote>, extra care may be needed to ensure that
<function>in_range</function>'s results agree with the normal
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:
To be precise, given any fixed values of
<replaceable>offset</replaceable> and
<replaceable>sub</replaceable>, then:
<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>.
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>.
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>.
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>.
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.
Analogous statements with inverted conditions hold when
<replaceable>less</replaceable> = false.
</para>
<para>
If the type being ordered (<type>type1</type>) is collatable,
the appropriate collation OID will be passed to
the <function>in_range</function> function, using the standard
If the type being ordered (<type>type1</type>) is collatable, the
appropriate collation OID will be passed to the
<function>in_range</function> function, using the standard
PG_GET_COLLATION() mechanism.
</para>
<para>
<function>in_range</function> functions need not handle NULL inputs, and
typically will be marked strict.
<function>in_range</function> functions need not handle NULL
inputs, and typically will be marked strict.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect1>
......
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