[Postgres-xc-developers] EXECUTE DIRECT queries with particular GROUP BY clause return strange binary results

[Masataka S. <pg...@gm...>]

Hi, all.

I got an error report that EXECUTE DIRECT queries with particular GROUP BY
clause return strange binary results and I made brief analysis.

The next query returns strang result.

EXECUTE DIRECT ON (datanode1) $$SELECT relkind FROM pg_class GROUP BY
relname, relkind$$;

It should return a result like Table A, but it returns a result like Table
B.

*Table A*

 relkind
---------
 i
 r
 v
 t
(4 rows)

*Table B*

 relkind
---------
 h

 \x18
 `

 8

 \x10
 X

 0
 x

 \x08
 P

 (
 p

 H

A query to a regular table work well.

cx=# create table tbl as select generate_series(1,10) as a,
generate_series(1,10) as b;
INSERT 0 10
cx=# execute direct on (datanode2) $$select b from tbl group by a,b$$;
 b
----
  7
 10
  4
  3
(4 rows)

On master_pg93_merge, this issue may cause psql disconnection. This query
doesn't make coordinator to be aborted.

cx=# execute direct on (datanode1) $$select tablename from
pg_catalog.pg_tables group by schemaname,tablename$$;
The connection to the server was lost. Attempting reset: Failed.
!>

And next queries return the right results.

# execute direct on (datanode1) $$select relkind from pg_class group
by relkind$$;
# execute direct on (datanode1) $$select relname, relkind from
pg_class group by relname, relkind$$;

It seems that this problem is produced when SELECT statement to pg_catalog
is issued and the selection target does not contain all of the columns
listed in the GROUP BY clause.

A datanode is returning the right result but a coordinator is returning
wrong result.
I think this issue is a bug of coordinator.

Regards.