On 18/08/2026 08:31, Andrei Lepikhov wrote:
> On 18/08/2026 06:56, David Rowley wrote:
>> Is delaying this until v20 fine for you?
> Yes, I can do it manually in pg_catalog for now - rewriting prosupport and
> setting the dependency in the pg_depend. There’s no rush - it’s just about
> keeping things tidy.
However, I noticed that it is not documented yet.
There are also three other prosupport requests that are not documented. A quick
search showed that documentation usually depends on the author, so it makes
sense to add it now.
Since each was introduced at a different time and serves a different purpose, I
suggest we start by documenting SupportRequestSimplifyAggref, as I am more
familiar with it - see the patch in attachment.
--
regards, Andrei Lepikhov,
pgEdge
From 08b9a1fdd6ab0ec67ccbe310df0bf0b64854b46c Mon Sep 17 00:00:00 2001
From: "Andrei V. Lepikhov" <[email protected]>
Date: Tue, 18 Aug 2026 14:29:50 +0200
Subject: [PATCH v0] Document the SupportRequestSimplifyAggref support request
The request has been in supportnodes.h since 42473b3b312, but
documentation was not updated, so the only description of it is the
header comment.
---
doc/src/sgml/xfunc.sgml | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml
index 2b8a11e7ad0..880edf24588 100644
--- a/doc/src/sgml/xfunc.sgml
+++ b/doc/src/sgml/xfunc.sgml
@@ -4241,6 +4241,22 @@ supportfn(internal) returns internal
normal execution of the target function.
</para>
+ <para>
+ Aggregate function calls can also be simplified during planning. For
+ example, <literal>COUNT(<replaceable>x</replaceable>)</literal> can be
+ replaced by <literal>COUNT(*)</literal>
+ when <replaceable>x</replaceable> is known not to be null. This can be
+ done by a support function that implements
+ the <literal>SupportRequestSimplifyAggref</literal> request type. The
+ support function will be called for each instance of its target aggregate
+ found in a query parse tree. If it finds that the particular call can be
+ replaced, it can build and return a new node, usually another aggregate
+ call, leaving the node it was given unmodified. As with
+ <literal>SupportRequestSimplify</literal>, it is the support function's
+ responsibility that the replacement be equivalent to normal execution of
the
+ target aggregate.
+ </para>
+
<para>
For target functions that return <type>boolean</type>, it is often useful
to estimate
the fraction of rows that will be selected by a <literal>WHERE</literal>
clause using that
--
2.55.0
