Feedback-ID: i0fe9450f:Fastmail
Date: Sun, 23 Mar 2025 09:47:31 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Christoph Berg <myon@debian.org>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	ma lz <ma100@hotmail.com>
Subject: Re: query_id: jumble names of temp tables for better
 pg_stat_statement UX
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On Sat, Mar 22, 2025 at 12:24:43PM -0400, Tom Lane wrote:
> I experimented with this trivial fix (shown in-line to keep the cfbot
> from thinking this is the patch-of-record):
>=20
> What's happening there is that there's an ALTER TABLE ADD COLUMN in
> the test, so the executions after the first one see more entries
> in eref->colnames and come up with a different jumble.  I think
> we probably don't want that behavior; we only want to jumble the
> table name.  So we'd still need the v3-0001 patch in some form to
> allow annotating RangeTblEntry.eref with a custom jumble method
> that'd only jumble the aliasname.

Alias.aliasname is not qualified, so it means that we'd begin to
assign the same query ID even if using two relations from two schemas
depending on what search_path assigns, no?  Say:
create schema popo1;
create schema popo2;
create table popo1.aa (a int, b int);
create table popo2.aa (a int, b int);
set search_path =3D 'popo1';
select count(*) from aa;
set search_path =3D 'popo2';
select count(*) from aa;

=3D# select query, calls from pg_stat_statements where
     query ~ 'select count';
          query          | calls
-------------------------+-------
 select count(*) from aa |     2
(1 row)

Perhaps that's OK because such queries use the same query string, but
just silencing the relid means that we'd lose the namespace reference
entirely, making the stats potentially fuzzier depending on the
workload.  On HEAD, one can guess the query ID with an EXPLAIN and a
search_path, as well, so currently it's possible to cross-check the=20
contents of pgss.  But we'd lose this possibility here..
--
Michael

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