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Commit2b5154b

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Extend ALTER OPERATOR to allow setting more optimization attributes.
Allow the COMMUTATOR, NEGATOR, MERGES, and HASHES attributes to be setby ALTER OPERATOR. However, we don't allow COMMUTATOR/NEGATOR to bechanged once set, nor allow the MERGES/HASHES flags to be unset onceset. Changes like that might invalidate plans already made, anddealing with the consequences seems like more trouble than it's worth.The main use-case we foresee for this is to allow addition of missedproperties in extension update scripts, such as extending an existingoperator to support hashing. So only transitions from not-set to setstates seem very useful.This patch also causes us to reject some incorrect cases that formerlyresulted in inconsistent catalog state, such as trying to set thecommutator of an operator to be some other operator that already has a(different) commutator.While at it, move the InvokeObjectPostCreateHook call for CREATEOPERATOR to not occur until after we've fixed up commutator or negatorlinks as needed. The previous ordering could only be justified bythinking of the OperatorUpd call as a kind of ALTER OPERATOR step;but we don't call InvokeObjectPostAlterHook therein. It seems betterto let the hook see the final state of the operator object.In the documentation, move the discussion of how to establishcommutator pairs from xoper.sgml to the CREATE OPERATOR ref page.Tommy Pavlicek, reviewed and editorialized a bit by meDiscussion:https://postgr.es/m/CAEhP-W-vGVzf4udhR5M8Bdv88UYnPrhoSkj3ieR3QNrsGQoqdg@mail.gmail.com
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13 files changed

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‎doc/src/sgml/ref/alter_operator.sgml

Lines changed: 81 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -30,7 +30,11 @@ ALTER OPERATOR <replaceable>name</replaceable> ( { <replaceable>left_type</repla
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ALTER OPERATOR <replaceable>name</replaceable> ( { <replaceable>left_type</replaceable> | NONE } , <replaceable>right_type</replaceable> )
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SET ( { RESTRICT = { <replaceable class="parameter">res_proc</replaceable> | NONE }
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| JOIN = { <replaceable class="parameter">join_proc</replaceable> | NONE }
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} [, ... ] )
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| COMMUTATOR = <replaceable class="parameter">com_op</replaceable>
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| NEGATOR = <replaceable class="parameter">neg_op</replaceable>
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| HASHES
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| MERGES
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} [, ... ] )
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</synopsis>
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</refsynopsisdiv>
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@@ -121,23 +125,95 @@ ALTER OPERATOR <replaceable>name</replaceable> ( { <replaceable>left_type</repla
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">com_op</replaceable></term>
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<listitem>
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<para>
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The commutator of this operator. Can only be changed if the operator
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does not have an existing commutator.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><replaceable class="parameter">neg_op</replaceable></term>
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<listitem>
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<para>
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The negator of this operator. Can only be changed if the operator does
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not have an existing negator.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>HASHES</literal></term>
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<listitem>
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<para>
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Indicates this operator can support a hash join. Can only be enabled and
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not disabled.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>MERGES</literal></term>
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<listitem>
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<para>
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Indicates this operator can support a merge join. Can only be enabled
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and not disabled.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>
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Refer to <xref linkend="xoper"/> and
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<xref linkend="xoper-optimization"/> for further information.
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</para>
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<para>
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Since commutators come in pairs that are commutators of each other,
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<literal>ALTER OPERATOR SET COMMUTATOR</literal> will also set the
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commutator of the <replaceable class="parameter">com_op</replaceable>
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to be the target operator. Likewise, <literal>ALTER OPERATOR SET
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NEGATOR</literal> will also set the negator of
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the <replaceable class="parameter">neg_op</replaceable> to be the
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target operator. Therefore, you must own the commutator or negator
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operator as well as the target operator.
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</para>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<para>
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Change the owner of a custom operator <literal>a @@ b</literal> for type <type>text</type>:
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<programlisting>
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ALTER OPERATOR @@ (text, text) OWNER TO joe;
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</programlisting></para>
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</programlisting>
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</para>
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<para>
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Change the restriction and join selectivity estimator functions of a custom operator <literal>a &amp;&amp; b</literal> for type <type>int[]</type>:
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Change the restriction and join selectivity estimator functions of a
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custom operator <literal>a &amp;&amp; b</literal> for
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type <type>int[]</type>:
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<programlisting>
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ALTER OPERATOR &amp;&amp; (_int4, _int4) SET (RESTRICT = _int_contsel, JOIN = _int_contjoinsel);
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</programlisting></para>
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ALTER OPERATOR &amp;&amp; (int[], int[]) SET (RESTRICT = _int_contsel, JOIN = _int_contjoinsel);
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</programlisting>
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</para>
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<para>
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Mark the <literal>&amp;&amp;</literal> operator as being its own
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commutator:
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<programlisting>
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ALTER OPERATOR &amp;&amp; (int[], int[]) SET (COMMUTATOR = &amp;&amp;);
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</programlisting>
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</para>
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</refsect1>
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‎doc/src/sgml/ref/create_operator.sgml

Lines changed: 63 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -104,15 +104,15 @@ CREATE OPERATOR <replaceable>name</replaceable> (
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</para>
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<para>
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The other clauses specify optional operator optimizationclauses.
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The other clauses specify optional operator optimizationattributes.
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Their meaning is detailed in <xref linkend="xoper-optimization"/>.
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</para>
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<para>
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To be able to create an operator, you must have <literal>USAGE</literal>
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privilege on the argument types and the return type, as well
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as <literal>EXECUTE</literal> privilege on the underlying function. If a
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commutator or negator operator is specified, you must ownthese operators.
115+
commutator or negator operator is specified, you must ownthose operators.
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</para>
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</refsect1>
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@@ -231,7 +231,67 @@ COMMUTATOR = OPERATOR(myschema.===) ,
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<title>Notes</title>
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<para>
234-
Refer to <xref linkend="xoper"/> for further information.
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Refer to <xref linkend="xoper"/> and <xref linkend="xoper-optimization"/>
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for further information.
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</para>
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<para>
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When you are defining a self-commutative operator, you just do it.
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When you are defining a pair of commutative operators, things are
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a little trickier: how can the first one to be defined refer to the
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other one, which you haven't defined yet? There are three solutions
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to this problem:
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<itemizedlist>
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<listitem>
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<para>
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One way is to omit the <literal>COMMUTATOR</literal> clause in the
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first operator that you define, and then provide one in the second
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operator's definition. Since <productname>PostgreSQL</productname>
251+
knows that commutative operators come in pairs, when it sees the
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second definition it will automatically go back and fill in the
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missing <literal>COMMUTATOR</literal> clause in the first
254+
definition.
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</para>
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</listitem>
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<listitem>
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<para>
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Another, more straightforward way is just to
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include <literal>COMMUTATOR</literal> clauses in both definitions.
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When <productname>PostgreSQL</productname> processes the first
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definition and realizes that <literal>COMMUTATOR</literal> refers to
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a nonexistent operator, the system will make a dummy entry for that
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operator in the system catalog. This dummy entry will have valid
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data only for the operator name, left and right operand types, and
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owner, since that's all that <productname>PostgreSQL</productname>
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can deduce at this point. The first operator's catalog entry will
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link to this dummy entry. Later, when you define the second
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operator, the system updates the dummy entry with the additional
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information from the second definition. If you try to use the dummy
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operator before it's been filled in, you'll just get an error
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message.
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</para>
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</listitem>
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<listitem>
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<para>
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Alternatively, both operators can be defined
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without <literal>COMMUTATOR</literal> clauses
281+
and then <command>ALTER OPERATOR</command> can be used to set their
282+
commutator links. It's sufficient to <command>ALTER</command>
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either one of the pair.
284+
</para>
285+
</listitem>
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</itemizedlist>
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288+
In all three cases, you must own both operators in order to mark
289+
them as commutators.
290+
</para>
291+
292+
<para>
293+
Pairs of negator operators can be defined using the same methods
294+
as for commutator pairs.
235295
</para>
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<para>

‎doc/src/sgml/xoper.sgml

Lines changed: 0 additions & 44 deletions
Original file line numberDiff line numberDiff line change
@@ -146,44 +146,6 @@ SELECT (a + b) AS c FROM test_complex;
146146
<literal>=</literal> operator must specify that it is valid, by marking the
147147
operator with commutator information.
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</para>
149-
150-
<para>
151-
When you are defining a self-commutative operator, you just do it.
152-
When you are defining a pair of commutative operators, things are
153-
a little trickier: how can the first one to be defined refer to the
154-
other one, which you haven't defined yet? There are two solutions
155-
to this problem:
156-
157-
<itemizedlist>
158-
<listitem>
159-
<para>
160-
One way is to omit the <literal>COMMUTATOR</literal> clause in the first operator that
161-
you define, and then provide one in the second operator's definition.
162-
Since <productname>PostgreSQL</productname> knows that commutative
163-
operators come in pairs, when it sees the second definition it will
164-
automatically go back and fill in the missing <literal>COMMUTATOR</literal> clause in
165-
the first definition.
166-
</para>
167-
</listitem>
168-
169-
<listitem>
170-
<para>
171-
The other, more straightforward way is just to include <literal>COMMUTATOR</literal> clauses
172-
in both definitions. When <productname>PostgreSQL</productname> processes
173-
the first definition and realizes that <literal>COMMUTATOR</literal> refers to a nonexistent
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operator, the system will make a dummy entry for that operator in the
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system catalog. This dummy entry will have valid data only
176-
for the operator name, left and right operand types, and result type,
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since that's all that <productname>PostgreSQL</productname> can deduce
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at this point. The first operator's catalog entry will link to this
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dummy entry. Later, when you define the second operator, the system
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updates the dummy entry with the additional information from the second
181-
definition. If you try to use the dummy operator before it's been filled
182-
in, you'll just get an error message.
183-
</para>
184-
</listitem>
185-
</itemizedlist>
186-
</para>
187149
</sect2>
188150

189151
<sect2 id="xoper-negator">
@@ -217,12 +179,6 @@ SELECT (a + b) AS c FROM test_complex;
217179
<literal>x &lt;&gt; y</literal>. This comes up more often than you might think, because
218180
<literal>NOT</literal> operations can be inserted as a consequence of other rearrangements.
219181
</para>
220-
221-
<para>
222-
Pairs of negator operators can be defined using the same methods
223-
explained above for commutator pairs.
224-
</para>
225-
226182
</sect2>
227183

228184
<sect2 id="xoper-restrict">

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