database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-09-02 04:21:28 +03:00
Code Activity

Extend ALTER OPERATOR to allow setting more optimization attributes.

Browse Source 
Allow the COMMUTATOR, NEGATOR, MERGES, and HASHES attributes to be set
by ALTER OPERATOR.  However, we don't allow COMMUTATOR/NEGATOR to be
changed once set, nor allow the MERGES/HASHES flags to be unset once
set.  Changes like that might invalidate plans already made, and
dealing with the consequences seems like more trouble than it's worth.
The main use-case we foresee for this is to allow addition of missed
properties in extension update scripts, such as extending an existing
operator to support hashing.  So only transitions from not-set to set
states seem very useful.

This patch also causes us to reject some incorrect cases that formerly
resulted in inconsistent catalog state, such as trying to set the
commutator of an operator to be some other operator that already has a
(different) commutator.

While at it, move the InvokeObjectPostCreateHook call for CREATE
OPERATOR to not occur until after we've fixed up commutator or negator
links as needed.  The previous ordering could only be justified by
thinking of the OperatorUpd call as a kind of ALTER OPERATOR step;
but we don't call InvokeObjectPostAlterHook therein.  It seems better
to let the hook see the final state of the operator object.

In the documentation, move the discussion of how to establish
commutator pairs from xoper.sgml to the CREATE OPERATOR ref page.

Tommy Pavlicek, reviewed and editorialized a bit by me

Discussion: https://postgr.es/m/CAEhP-W-vGVzf4udhR5M8Bdv88UYnPrhoSkj3ieR3QNrsGQoqdg@mail.gmail.com
This commit is contained in:
Tom Lane
2023-10-20 12:28:38 -04:00
parent dcd4454590
commit 2b5154beab
13 changed files with 871 additions and 207 deletions
Download Patch File Download Diff File Expand all files Collapse all files

86
doc/src/sgml/ref/alter_operator.sgml
View File

@@ -30,7 +30,11 @@ ALTER OPERATOR <replaceable>name</replaceable> ( { <replaceable>left_type</repla
ALTER OPERATOR <replaceable>name</replaceable> ( { <replaceable>left_type</replaceable> | NONE } , <replaceable>right_type</replaceable> )
SET ( { RESTRICT = { <replaceable class="parameter">res_proc</replaceable> | NONE }
| JOIN = { <replaceable class="parameter">join_proc</replaceable> | NONE }
} [, ... ] )
| COMMUTATOR = <replaceable class="parameter">com_op</replaceable>
| NEGATOR = <replaceable class="parameter">neg_op</replaceable>
| HASHES
| MERGES
} [, ... ] )
</synopsis>
</refsynopsisdiv>
@@ -121,9 +125,69 @@ ALTER OPERATOR <replaceable>name</replaceable> ( { <replaceable>left_type</repla
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">com_op</replaceable></term>
<listitem>
<para>
The commutator of this operator. Can only be changed if the operator
does not have an existing commutator.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">neg_op</replaceable></term>
<listitem>
<para>
The negator of this operator. Can only be changed if the operator does
not have an existing negator.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>HASHES</literal></term>
<listitem>
<para>
Indicates this operator can support a hash join. Can only be enabled and
not disabled.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>MERGES</literal></term>
<listitem>
<para>
Indicates this operator can support a merge join. Can only be enabled
and not disabled.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Notes</title>
<para>
Refer to <xref linkend="xoper"/> and
<xref linkend="xoper-optimization"/> for further information.
</para>
<para>
Since commutators come in pairs that are commutators of each other,
<literal>ALTER OPERATOR SET COMMUTATOR</literal> will also set the
commutator of the <replaceable class="parameter">com_op</replaceable>
to be the target operator. Likewise, <literal>ALTER OPERATOR SET
NEGATOR</literal> will also set the negator of
the <replaceable class="parameter">neg_op</replaceable> to be the
target operator. Therefore, you must own the commutator or negator
operator as well as the target operator.
</para>
</refsect1>
<refsect1>
<title>Examples</title>
@@ -131,13 +195,25 @@ ALTER OPERATOR <replaceable>name</replaceable> ( { <replaceable>left_type</repla
Change the owner of a custom operator <literal>a @@ b</literal> for type <type>text</type>:
<programlisting>
ALTER OPERATOR @@ (text, text) OWNER TO joe;
</programlisting></para>
</programlisting>
</para>
<para>
Change the restriction and join selectivity estimator functions of a custom operator <literal>a &amp;&amp; b</literal> for type <type>int[]</type>:
Change the restriction and join selectivity estimator functions of a
custom operator <literal>a &amp;&amp; b</literal> for
type <type>int[]</type>:
<programlisting>
ALTER OPERATOR &amp;&amp; (_int4, _int4) SET (RESTRICT = _int_contsel, JOIN = _int_contjoinsel);
</programlisting></para>
ALTER OPERATOR &amp;&amp; (int[], int[]) SET (RESTRICT = _int_contsel, JOIN = _int_contjoinsel);
</programlisting>
</para>
<para>
Mark the <literal>&amp;&amp;</literal> operator as being its own
commutator:
<programlisting>
ALTER OPERATOR &amp;&amp; (int[], int[]) SET (COMMUTATOR = &amp;&amp;);
</programlisting>
</para>
</refsect1>