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

Στις 10/12/23 00:08, ο/η Tom Lane έγραψε:
> Achilleas Mantzios<a(dot)mantzios(at)cloud(dot)gatewaynet(dot)com> writes:
>> Hi again, I am puzzled with your observations, this is what I get with
>> psql straight against PostgreSQL no pgbouncer involved :
>> command :
>> psql "postgresql://amantzio(at)localhost:5432/dynacom?application_name="
>> ...
>> public.S....is_superuser.on.S....application_name..S...&default_transaction_read_only.off.S....scram_iterations.4096.S....DateStyle.ISO,
> ^^^^^^^^^^^^^^^^^^^^^^^
>
> I see the report of application_name with an empty-string value right
> there.
The report, ok, I am talking about the startup packet. Please read below.
>
>> the client does not send the application_name
> I do not know what you mean by that, but maybe your client code has
> some special-case behavior for an empty string?

The above  was plain vanilla psql, nothing special. Let me show the two
startup packets (psql -> pgsql) in each case :

case 1: psql
"postgresql://amantzio(at)localhost:5432/dynacom?application_name="

23:29:00.415726 IP localhost.31933 > localhost.postgresql: Flags [P.],
seq 1:62, ack 1, win 1277, options [nop,nop,TS val 1343970026 ecr
3656173586], length 61
E(dot)(dot)q(dot)(dot)(at)(dot)@...........|..8...k2.M......e.....
*P.Z........=....user.amantzio.database.dynacom.client_encoding.UTF8..*

case 2: psql
"postgresql://amantzio(at)localhost:5432/dynacom?application_name=''"

23:31:45.583486 IP localhost.13693 > localhost.postgresql: Flags [P.],
seq 1:82, ack 1, win 1277, options [nop,nop,TS val 300427204 ecr
2261783934], length 81
E(dot)(dot)(dot)(dot)(dot)(at)(dot)@...........5}.8.`Pc...1.....y.....
*..'....~...Q....user.amantzio.database.dynacom.application_name.''.client_encoding.UTF8..*

So, in the first case (application_name=) , there is not explicit
setting of application_name by the client in the startup packet, whereas
in the second case (application_name='') there is.

On this observation we based our temporary solution for the core problem
described in this thread : Our trick to workaround this , is to define a
dummy string e.g. '' in the startup packet, followed by an explicit SET
application_name='OurApplicationName' so that the backend always
receives two consecutive settings, and always understands the 2nd as a
changed value, so it always reports the correct application_name back to
the pgbouncer .

>
> regards, tom lane

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