Message-ID: <0028c29e-26f3-48e7-9201-f94d2579b9ba@cloud.gatewaynet.com>
Date: Sat, 9 Dec 2023 08:52:36 +0200
MIME-Version: 1.0
Subject: Re: application_name backend (not) reporting back to the client :
 pgbouncer, PgSQL 16.1, pgbouncer 1.21.0
Content-Language: en-US
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-admin@lists.postgresql.org, nc@gatewaynet.com,
 Achilleas Mantzios <itdev@gatewaynet.com>
References: <e33e0231-77d7-4dd7-4b7c-97af1d0e091b@cloud.gatewaynet.com>
 <1436714.1702046865@sss.pgh.pa.us>
 <06bf30c8-371e-5575-e1cc-a6dc1140b8af@cloud.gatewaynet.com>
 <1454680.1702054572@sss.pgh.pa.us>
 <ff2ee637-f3b6-424d-8ebf-d7cb089487de@cloud.gatewaynet.com>
 <1552992.1702076062@sss.pgh.pa.us>
From: Achilleas Mantzios <a.mantzios@cloud.gatewaynet.com>
In-Reply-To: <1552992.1702076062@sss.pgh.pa.us>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Archived-At: 
 <https://www.postgresql.org/message-id/0028c29e-26f3-48e7-9201-f94d2579b9ba%40cloud.gatewaynet.com>
Precedence: bulk

Στις 9/12/23 00:54, ο/η Tom Lane έγραψε:
> Achilleas Mantzios <a.mantzios@cloud.gatewaynet.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