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

[Kelly Burkhart]

It does trigger a failover and worse, once a backend has been
terminated with SIGINT, no new connections can be established through
the pool until the whole pool is restarted.  That's exactly the
problem we are trying to solve.

-K

On Sun, Jan 2, 2011 at 3:54 AM, Tatsuo Ishii <ishii at sraoss.co.jp> wrote:
>> 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.
>
> If the particular use is canceling the long running query, why don't
> you use query cancel? It can be done by signaling PostgreSQL backend
> process with SIGINT signal. This does not trigger failover of
> pgpool-II of course.
> --
> Tatsuo Ishii
> SRA OSS, Inc. Japan
> English: http://www.sraoss.co.jp/index_en.php
> Japanese: http://www.sraoss.co.jp
>