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

Achilleas Mantzios <a.mantzios@cloud.gatewaynet.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@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@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..q..@.@...........|..8...k2.M......e.....
P.Z........=....user.amantzio.database.dynacom.client_encoding.UTF8..

case 2:  psql "postgresql://amantzio@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.....@.@...........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