Re: [HACKERS] logical replication and PANIC during shutdowncheckpoint in publisher

On 4/19/17 01:45, Michael Paquier wrote:
> On Tue, Apr 18, 2017 at 3:27 AM, Peter Eisentraut
> <peter.eisentraut@2ndquadrant.com> wrote:
>> I'd imagine the postmaster would tell the walsender that it has started
>> shutdown, and then the walsender would reject $certain_things.  But I
>> don't see an existing way for the walsender to know that shutdown has
>> been initiated.  SIGINT is still free ...
> 
> The WAL sender receives SIGUSR2 from the postmaster when shutdown is
> initiated, so why not just rely on that and issue an ERROR when a
> client attempts to create or drop a new slot, setting up
> walsender_ready_to_stop unconditionally? It seems to me that the issue
> here is the delay between the moment SIGTERM is acknowledged by the
> WAL sender and the moment CREATE_SLOT is treater. An idea with the
> attached...

I think the problem with a signal-based solution is that there is no
feedback.  Ideally, you would wait for all walsenders to acknowledge the
receipt of SIGUSR2 (or similar) and only then proceed with the shutdown
checkpoint.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services