Hello!
Last time, I forgot to attach the patches.
The problem still persists in the 17.3 release.
Solution One
============
The simplest way to fix the problem is to place the scalar field used in the query ID calculation
between similar subnodes.
A patch for this solution is attached below (0001-Query-ID-Calculation-Fix-Variant-A.patch).
Solution Two
============
Alternatively, we can change the hash sum when we encounter an empty node.
This approach may impact performance but will protect us from such errors in the future.
A patch for this solution is attached below (0001-Query-ID-Calculation-Fix-Variant-B.patch).
======
SELECT version();
version
-------------------------------------------------------------------------------------------------
PostgreSQL 17.3 on x86_64-pc-linux-gnu, compiled by gcc (Debian 12.2.0-14) 12.2.0, 64-bit
SET compute_query_id = on;
/* LIMIT / OFFSET */
EXPLAIN (VERBOSE) SELECT "oid" FROM pg_class LIMIT 1;
QUERY PLAN
----------------------------------------------------------------------------
Limit (cost=0.00..0.04 rows=1 width=4)
Output: oid
-> Seq Scan on pg_catalog.pg_class (cost=0.00..18.15 rows=415 width=4)
Output: oid
Query Identifier: 5185884322440896420
EXPLAIN (VERBOSE) SELECT "oid" FROM pg_class OFFSET 1;
QUERY PLAN
----------------------------------------------------------------------------
Limit (cost=0.04..18.15 rows=414 width=4)
Output: oid
-> Seq Scan on pg_catalog.pg_class (cost=0.00..18.15 rows=415 width=4)
Output: oid
Query Identifier: 5185884322440896420
/* DISTINCT / ORDER BY */
EXPLAIN (VERBOSE) SELECT DISTINCT "oid" FROM pg_class;
QUERY PLAN
------------------------------------------------------------------------------------------------------------
Unique (cost=0.27..23.54 rows=415 width=4)
Output: oid
-> Index Only Scan using pg_class_oid_index on pg_catalog.pg_class (cost=0.27..22.50 rows=415 width=4)
Output: oid
Query Identifier: 751948508603549510
EXPLAIN (VERBOSE) SELECT "oid" FROM pg_class ORDER BY "oid";
QUERY PLAN
------------------------------------------------------------------------------------------------------
Index Only Scan using pg_class_oid_index on pg_catalog.pg_class (cost=0.27..22.50 rows=415 width=4)
Output: oid
Query Identifier: 751948508603549510
