Re: Printing backtrace of postgres processes

On Sat, Jan 16, 2021 at 11:10 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> Hi,
>
> On Sat, Jan 16, 2021, at 09:34, vignesh C wrote:
> > On Sat, Jan 16, 2021 at 1:40 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > >
> > > On 2021-01-15 09:53:05 +0100, Peter Eisentraut wrote:
> > > > On 2020-12-08 10:38, vignesh C wrote:
> > > > > I have implemented printing of backtrace based on handling it in
> > > > > CHECK_FOR_INTERRUPTS. This patch also includes the change to allow
> > > > > getting backtrace of any particular process based on the suggestions.
> > > > > Attached patch has the implementation for the same.
> > > > > Thoughts?
> > > >
> > > > Are we willing to use up a signal for this?
> > >
> > > Why is a full signal needed? Seems the procsignal infrastructure should
> > > suffice?
> >
> > Most of the processes have access to ProcSignal, for these processes
> > printing of callstack signal was handled by using ProcSignal. Pgstat
> > process & syslogger process do not have access to ProcSignal,
> > multiplexing with SIGUSR1 is not possible for these processes. So I
> > handled the printing of callstack for pgstat process & syslogger using
> > the SIGUSR2 signal.
> > This is because shared memory is detached before pgstat & syslogger
> > process is started by using the below:
> > /* Drop our connection to postmaster's shared memory, as well */
> > dsm_detach_all();
> > PGSharedMemoryDetach();
>
> Sure. But why is it important enough to support those that we are willing to dedicate a signal to the task? Their backtraces aren't often interesting, so I think we should just ignore them here.

Thanks for your comments Andres, I will ignore it for the processes
which do not have access to ProcSignal. I will make the changes and
post a patch for this soon.

Regards,
Vignesh
EnterpriseDB: http://www.enterprisedb.com