Segmentation fault on EXPLAIN of a query with LEFT JOIN to a distributed table and correlated subqueries in Citus 14.0.0 (PostgreSQL 18.1)

[duerwuyi]

Description

I found a reproducible backend crash in Citus 14.0.0.

On my setup, EXPLAIN of the query below terminates the client backend with signal 11: Segmentation fault, which then forces PostgreSQL recovery. The same testcase does not reproduce on Citus 13.0.2.

The crash happens during EXPLAIN, so this appears to be in planning / distributed planning rather than execution.

Environment

• PostgreSQL 18.1
• Citus 14.0.0

select version();
PostgreSQL 18.1 (Debian 18.1-1.pgdg13+2) on x86_64-pc-linux-gnu, compiled by gcc (Debian 14.2.0-19) 14.2.0, 64-bit

select citus_version();
Citus 14.0.0 on x86_64-pc-linux-gnu, compiled by gcc (Debian 14.2.0-19) 14.2.0, 64-bit

Version comparison

• Reproduces on: Citus 14.0.0
• Does not reproduce on: Citus 13.0.2

Minimal schema

Only t22 is distributed, and it is distributed by colocated_key.
The other tables are regular local tables.

DROP TABLE IF EXISTS t4 CASCADE;
DROP TABLE IF EXISTS t5 CASCADE;
DROP TABLE IF EXISTS t7 CASCADE;
DROP TABLE IF EXISTS t2 CASCADE;
DROP TABLE IF EXISTS t22 CASCADE;

CREATE TABLE t4 (
    vkey integer,
    pkey integer,
    c30 integer,
    c31 integer,
    c32 text
);

CREATE TABLE t5 (
    vkey integer,
    pkey integer,
    c33 text,
    c34 integer,
    c35 integer,
    c36 timestamp without time zone
);

CREATE TABLE t7 (
    vkey integer,
    pkey integer,
    c45 integer,
    c46 integer,
    c47 integer,
    c48 numeric,
    c49 integer
);

CREATE TABLE t2 (
    vkey integer,
    pkey integer,
    c15 numeric,
    c16 timestamp without time zone,
    c17 text,
    c18 text,
    c19 timestamp without time zone,
    c20 timestamp without time zone,
    c21 integer
);

CREATE TABLE t22 (
    vkey integer,
    pkey integer,
    c37 numeric,
    c38 text,
    c39 numeric,
    c40 numeric,
    c41 numeric,
    c42 integer,
    c43 timestamp without time zone,
    c44 numeric,
    colocated_key numeric
);

SELECT create_distributed_table('t22', 'colocated_key');

## Query to reproduce

```sql
select
  70 as c_0
from
  (
    select
      (
        exists (
          select
            ref_5.c33 as c_0
          from
            t5 as ref_5
          where
            (make_timestamp(2001, 7, 13, 17, 53, 31)) = (ref_1.c43)
        )
      ) as c_0
    from
      (
        t4 as ref_0
        left outer join t22 as ref_1
          on (ref_0.vkey = ref_1.vkey)
      )
    where
      (
        (ref_0.c31) >= (
          select
            ref_1.pkey as c_0
          from
            t2 as ref_2
          where
            (true) < ((ref_2.c17) ^@ (ref_0.c32))
          order by
            c_0 desc
          limit 1
        )
      ) in (
        select
          (ref_1.c40) <= (ref_1.c37) as c_0
        from
          t7 as ref_4
        where
          not ((ref_1.c40) <> (ref_1.c41))
      )
  ) as subq_0
where
  (TRUE) < (TRUE);

log

LOG:  client backend (PID 114) was terminated by signal 11: Segmentation fault
DETAIL:  Failed process was running: EXPLAIN select ...
LOG:  terminating any other active server processes
LOG:  all server processes terminated; reinitializing
LOG:  database system was interrupted; automatic recovery in progress

Expected behavior

EXPLAIN should either:

successfully produce a plan, or
return a normal SQL/planning error if this query shape is unsupported.

It should not crash the backend.