Thread: A server crash with a SQL procedure returning a user-defined type on 14.8

A server crash with a SQL procedure returning a user-defined type on 14.8

From

Yahor Yuzefovich

Date:

12 March, 01:19:37

Hello there,

I believe I encountered a bug with the following reproduction steps:

CREATE TYPE typ AS (a INT, b INT); CREATE PROCEDURE p_udt(OUT typ) AS $$ SELECT (1, 2); $$ LANGUAGE SQL; CALL p_udt(NULL);

which results in a server crash on version 14.8:

server closed the connection unexpectedly

This probably means the server terminated abnormally

before or while processing the request.

The connection to the server was lost. Attempting reset: WARNING: terminating connection because of crash of another server process

DETAIL: The postmaster has commanded this server process to roll back the current transaction and exit, because another server process exited abnormally and possibly corrupted shared memory.

HINT: In a moment you should be able to reconnect to the database and repeat your command.

Failed.

Best,

Yahor Yuzefovich

Re: A server crash with a SQL procedure returning a user-defined type on 14.8

From

Tom Lane

Date:

12 March, 22:50:43

Yahor Yuzefovich <yahor@cockroachlabs.com> writes:
> CREATE TYPE typ AS (a INT, b INT); CREATE PROCEDURE p_udt(OUT typ) AS $$
> SELECT (1, 2); $$ LANGUAGE SQL; CALL p_udt(NULL);

Thanks for the report.  What seems to be happening is that functions.c
is getting confused as to whether it should return a record containing
a record, or just a record.  check_sql_fn_retval explains:

         * If the target list has one non-junk entry, and that expression has
         * or can be coerced to the declared return type, take it as the
         * result.  This allows, for example, 'SELECT func2()', where func2
         * has the same composite return type as the function that's calling
         * it.  This provision creates some ambiguity --- maybe the expression
         * was meant to be the lone field of the composite result --- but it
         * works well enough as long as we don't get too enthusiastic about
         * inventing coercions from scalar to composite types.

As far as I know, that is fine for functions.  But it's not fine for
procedures: those are marked as returning RECORD if there are any
output parameters at all, and the code for CALL expects that it's
going to get back a record containing one column per output parameter,
so we can't flatten that into a record containing two ints.
This has been busted since we invented procedures, I think.

This is easy to fix if we add a parameter to check_sql_fn_retval
indicating whether we're considering a function or a procedure.
While that's not problematic in HEAD, I'm worried that there might
be external callers of that function in the back branches.  I guess
we can use the old trick of making the existing function into a
wrapper in the back branches.

            regards, tom lane