Re: BUG #16754: When using LLVM and parallel queries aborted all session by pg_cancel_backend.

Hi,

On 2020-12-07 08:58:18 +0000, Shinoda, Noriyoshi (PN Japan FSIP) wrote:
> Thanks for the comment.
> I newly cloned the latest version 13.1 source and then rebuilt it. The
> segmentation fault has recurred.I tried the backtrace feature, but it
> didn't work.

What exactly do you mean by that? You attached to the worker with a
debugger, and you didn't get a backtrace once it crashed? Same with a
core file? Or were you hoping for the segfault to automatically
generate a backtrace?

The easist way would be to enable core files with 'ulimit -c unlimited'
in the shell you start postgres in, and to set the
'jit_debugging_support=1' option. Then, once the crash happend, you
should be able to find a core file.

You then can inspect that core file with
gdb /path/to/postgres -core /path/to/core

and execute 'bt' inside.

> The function specification may not have been good.

Which function's specification?

> Segmentation faults do not always occur, but occasionally after running pg_cancel_backend several times.
> Also, it only seems to happen if I canceled the parallel worker process.

I tried this a couple hundred times without success.

Greetings,

Andres Freund