From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Achilleas Mantzios <a(dot)mantzios(at)cloud(dot)gatewaynet(dot)com> |
Cc: | pgsql-admin(at)lists(dot)postgresql(dot)org, nc(at)gatewaynet(dot)com, Achilleas Mantzios <itdev(at)gatewaynet(dot)com> |
Subject: | Re: application_name backend (not) reporting back to the client : pgbouncer, PgSQL 16.1, pgbouncer 1.21.0 |
Date: | 2023-12-08 22:54:22 |
Message-ID: | 1552992.1702076062@sss.pgh.pa.us |
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Lists: | pgsql-admin |
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.
> 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.
regards, tom lane
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