Subject: Re: BUG #16976: server crash when deleting via a trigger on a foreign
 table
To: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-bugs@lists.postgresql.org,
 PG Bug reporting form <noreply@postgresql.org>
References: <16976-abe0cb88252bc02e@postgresql.org>
 <756273.1619012414@sss.pgh.pa.us>
From: Herwig Goemans <herwig.goemans@gmail.com>
Message-ID: <813ebc08-8f81-4efe-a5f2-caac938b7741@gmail.com>
Date: Thu, 22 Apr 2021 12:09:44 +0200
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Hi,


I tried it again. With a previous test the trigger did not exists, that 
is why it worked.

Anyway, with the trigger in place we encounter PG server crashes.

I am having trouble collection a trace file because when I attach gdb to 
the process:

0x00007f99b46f7a07 in epoll_wait (epfd=5, events=0x561321b40630, 
maxevents=maxevents@entry=1, timeout=timeout@entry=-1) at 
../sysdeps/unix/sysv/linux/epoll_wait.c:30
30      ../sysdeps/unix/sysv/linux/epoll_wait.c: No such file or directory.
(gdb) quit

or

Reading symbols from /lib/x86_64-linux-gnu/libnss_files.so.2...Reading 
symbols from 
/usr/lib/debug//lib/x86_64-linux-gnu/libnss_files-2.27.so...done.
done.
0x00007fd77dc3343e in __libc_read (fd=0, buf=0x7ffc49e20010, nbytes=1) 
at ../sysdeps/unix/sysv/linux/read.c:27
27      ../sysdeps/unix/sysv/linux/read.c: No such file or directory.
(gdb) quit
A debugging session is active.

         Inferior 1 [process 35694] will be detached.

And I cannot execute anything in the attached (psql) process,

it complains about a file not found , always in sysdeps. ( i do not find 
this directory on the server)

Anyway when the trigger is fired, it crashes the server.

I can delete on the foreign table directly and I can delete on the 
foreign table with a function that returns void instead of trigger. all 
that works fine.

The function is:

  CREATE OR REPLACE FUNCTION metadblucht.test_herwig(p_enh_id int)
  RETURNS void
  LANGUAGE plpgsql
AS $function$
             BEGIN
                 delete from informix.t_water_eenheid
                 where enh_id = p_enh_id;
             END;
         $function$
;


When I run this function, it works fine.

SELECT metadblucht.test_herwig(38);

and the record is deleted from the foriegn table.

I can delete from the foreign table directly:

delete from informix.t_water_eenheid  where enh_id = 40;

that works fine as well.


Can you continue zith this information or do you still need the trace 
file. I have no idea what I can do to resolve the issue with sysdeps not 
on the server.


Kind regards,


Herwig


On 21/04/2021 15:40, Tom Lane wrote:
>> I have experienced a server crash when deleting from a table that ahs a
>> before trigger on it. The before trigger calls a function that deletes from
>> a foreign (informix) table.
> Hm, can you get a stack trace from that?
>
> https://wiki.postgresql.org/wiki/Generating_a_stack_trace_of_a_PostgreSQL_backend
>
> It seems fairly likely that the bug is in whatever FDW you're using
> rather than in core Postgres.  A stack trace would help to
> confirm or refute that.
>
> 			regards, tom lane