Re: [HACKERS] Terminating a backend

Bruce Momjian wrote:
> Bruce Momjian wrote:
> > I have an idea for this TODO item:
> >
> >     * Allow administrators to safely terminate individual sessions either
> >       via an SQL function or SIGTERM
> >
> >       Lock table corruption following SIGTERM of an individual backend
> >       has been reported in 8.0.  A possible cause was fixed in 8.1, but
> >       it is unknown whether other problems exist.  This item mostly
> >       requires additional testing rather than of writing any new code.
> >
> >       http://archives.postgresql.org/pgsql-hackers/2006-08/msg00174.php
> >
> > When we get the termination signal, why can't we just set a global
> > boolean, do a query cancel, and in the setjmp() code block check the
> > global and exit --- at that stage we know we have released all locks and
> > can exit cleanly.
>
> I have implemented this idea with the attached patch.

One problem I have with my patch is that SIGTERM is currently used by
the postmaster to shut down backends.  Now because the postmaster knows
that all backend are terminating, it can accept a dirtier shutdown than
one where we are terminating just one backend and the rest are going to
keep running.  The new SIGTERM coding is going to exit a backend only in
a place where cancel is checked.

I need some thoughts in this area.

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

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