"RuntimeMergeAppend child's targetlist doesn't match RuntimeMergeAppend" error occurs on some sql

[ChenHuajun]

Problem description

When execute some sql，the following error occurs

ERROR:  RuntimeMergeAppend child's targetlist doesn't match RuntimeMergeAppend

The following sql can reproduct this problem

CREATE EXTENSION pg_pathman;
CREATE TABLE partitioned_table(id INT NOT NULL, payload int);
create index on partitioned_table(payload);

INSERT INTO partitioned_table
SELECT generate_series(1, 1000), random();

SELECT create_hash_partitions('partitioned_table', 'id', 10);

CREATE TABLE some_table AS SELECT generate_series(1, 100) AS VAL;

set enable_seqscan =f;

explain analyze
SELECT max(id),payload FROM partitioned_table 
WHERE id = (SELECT * FROM some_table LIMIT 1)
group by payload;

And, when change max(id),payload to payload,max(id) in select list, this sql executing is ok.

explain analyze
SELECT payload,max(id) FROM partitioned_table 
WHERE id = (SELECT * FROM some_table LIMIT 1)
group by payload;

and the plan is as following:

                                                                            QUERY PLAN                                                                             
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
 GroupAggregate  (cost=10000000000.17..10000000087.88 rows=11 width=8) (actual time=0.134..0.134 rows=1 loops=1)
   Group Key: partitioned_table.payload
   InitPlan 1 (returns $0)
     ->  Limit  (cost=10000000000.00..10000000000.01 rows=1 width=4) (actual time=0.020..0.021 rows=1 loops=1)
           ->  Seq Scan on some_table  (cost=10000000000.00..10000000035.50 rows=2550 width=4) (actual time=0.019..0.019 rows=1 loops=1)
   ->  Custom Scan (RuntimeMergeAppend)  (cost=0.16..87.71 rows=11 width=8) (actual time=0.116..0.127 rows=1 loops=1)
         Prune by: (partitioned_table.id = $0)
         Sort Key: partitioned_table.payload
         ->  Index Scan using partitioned_table_0_payload_idx on partitioned_table_0  (cost=0.15..87.70 rows=11 width=8) (actual time=0.069..0.079 rows=1 loops=1)
               Filter: (id = $0)
               Rows Removed by Filter: 97
 Planning time: 0.581 ms
 Execution time: 0.212 ms
(13 rows)

Environment

postgres=# SELECT * FROM pg_extension;
  extname   | extowner | extnamespace | extrelocatable | extversion |   extconfig   | extcondition 
------------+----------+--------------+----------------+------------+---------------+--------------
 plpgsql    |       10 |           11 | f              | 1.0        |               | 
 pg_pathman |       10 |         2200 | f              | 1.5        | {16702,16713} | {"",""}
(2 rows)

postgres=# SELECT version();
                                                 version                                                  
----------------------------------------------------------------------------------------------------------
 PostgreSQL 10.10 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-36), 64-bit
(1 row)

And, I had tried in PG 10.10 and PG 11.3, only PG 10.10 occurs.

• PG 10.10 + pathman 1.5.8 NG
• PG 11.3 + pathman 1.5.8 OK