Re: application_name backend (not) reporting back to the client : pgbouncer, PgSQL 16.1, pgbouncer 1.21.0

Στις 9/12/23 00:54, ο/η Tom Lane έγραψε:
> Achilleas Mantzios <a(dot)mantzios(at)cloud(dot)gatewaynet(dot)com> writes:
>> the trick is to have "application_name=" with no value.  This causes the
>> server to not set application_name initially.
> No, that sets it to an empty string, while application_name='' sets
> it to two single quotes, according to the testing I did. In either
> case, that value will be reported to the client as the active value
> during connection start. Then the subsequent SET causes a new
> report, but (since v14) only if the value being set is different.

Thank you Tom, now I see we have a different behavior, I have uploaded a
video that demonstrates my case : https://youtu.be/qcrVsFszV0Y

I didn't have the time to fire up wireshark/tcpdump or debugger thought
(I should).

>
>> Please check the scenario
>> Client C1 connects to S1, sets application_name. BEGINS, COMMITS, the
>> server gets freed to server the next client.
>> Client C2 connects to the same S1, sets application_name, and gets no
>> report back. So it stays with application_name empty. Then this breaks
>> the application.
>> How could pgbouncer prevent this from happening ?
> pgbouncer would have to regurgitate the latest ParameterStatus
> messages to the new client (during its faked-up initial connection
> handshake) to ensure everything's synchronized correctly.
> If for some reason it's not doing that, that would be a pretty
> serious bug if you ask me, since clients might be relying on
> hearing the truth about settings like client_encoding. Since
> the whole point of pgbouncer is that the backend doesn't know
> a new client has been slotted in, it's not clear to me how or
> why the backend should solve this.
You helped a great deal! It is time I open an issue on the pgbouncer
project.
>
> regards, tom lane

--
Achilleas Mantzios
IT DEV - HEAD
IT DEPT
Dynacom Tankers Mgmt