[Pgpool-general] Unable to accept new connection after terminating pgpool backend process

[Kelly Burkhart]

On Wed, Dec 29, 2010 at 7:41 AM, Tatsuo Ishii <ishii at sraoss.co.jp> wrote:
>>>> What we like to have is the ability to:
>>>> - Treat the error code got back from pg_terminate_backend (or the kill
>>>> command) as a regular disconnect
>>>
>>> It isn't possible without changing PostgreSQL itself.
>>
>> Can you please explain why?  If we kill -INT a backend postgres
>> process, it doesn't take the whole database cluster down, it shouldn't
>> take the whole pool down either.  The fact that it does is a bug in
>> pg_pool IMO.
>
> The problem is PostgreSQL returns exactly the same error code when
> postmaster goes down. See:
>
> http://archives.postgresql.org/pgsql-hackers/2010-05/msg00629.php
>

OK, I'm not familiar enough with postgres code to understand why
killing a single backend should return the same code to client as a
controlled shutdown of the database.  However, if the DB is shutdown,
*every* pool process will get the error code, in our case only the one
running the query that needed to be stopped.

Since ADMIN_SHUTDOWN_ERROR_CODE is sent by the backend for two
completely different events, perhaps the answer is to not test for it.
 If a single backend goes down you send the error code to the client
and disconnect.  If all backends go down, that's effectively the same
as the database machine crashing.

-K