Terminating a backend

oikBruce Momjian wrote:
> Bruce Momjian wrote:
> > > > 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 have a idea --- to have pg_terminate_backend() set a PGPROC boolean
> and then send a query cancel signal to the backend --- the backend can
> then check the boolean and exit if required. I will work on a new
> version of this patch tomorrow/Monday.

Updated patch attached. I didn't modify SIGTERM at all but set a PRPROC
boolean and piggybacked on SIGINT. I think I got the PGPROC locking
right. I had to split apart pg_signal_backend() so I could do the
permission and pid checks independent of the signalling, because I
pg_terminate_backend() needs to check, then set the PGPROC variable,
then send the signal.

I also added an administration doc mention about when to use
pg_terminate_backend().

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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