Thread: BUG #18754: Logical replication cannot restart if client sent a copyDone

The following bug has been logged on the website:

Bug reference:      18754
Logged by:          S.A.N
Email address:      ua.san.alex@gmail.com
PostgreSQL version: 17.2
Operating system:   MacOS
Description:

Logical replication cannot restart if the client sent a copyDone, because
the streamingDoneReceiving variable is not reassigned to false in function
StartLogicalReplication, this only happens when physical replication in
function StartReplication
https://github.com/postgres/postgres/blob/master/src/backend/replication/walsender.c#L906

I am writing a logical replication client, sometimes I need to exit copy
mode to send simple SQL queries.

I send copyDone, everything works correctly, I can perform SQL queries, but
then I need to return to replication mode, the START_REPLICATION command
will always completed immediately, because the streamingDoneReceiving
backend variable remains in true, I think it should be redefined in false
when starting logical replication.

Thanks.

On Fri, 27 Dec 2024 at 20:44, PG Bug reporting form
<noreply@postgresql.org> wrote:
>
> The following bug has been logged on the website:
>
> Bug reference:      18754
> Logged by:          S.A.N
> Email address:      ua.san.alex@gmail.com
> PostgreSQL version: 17.2
> Operating system:   MacOS
> Description:
>
> Logical replication cannot restart if the client sent a copyDone, because
> the streamingDoneReceiving variable is not reassigned to false in function
> StartLogicalReplication, this only happens when physical replication in
> function StartReplication
> https://github.com/postgres/postgres/blob/master/src/backend/replication/walsender.c#L906
>
> I am writing a logical replication client, sometimes I need to exit copy
> mode to send simple SQL queries.
>
> I send copyDone, everything works correctly, I can perform SQL queries, but
> then I need to return to replication mode, the START_REPLICATION command
> will always completed immediately, because the streamingDoneReceiving
> backend variable remains in true, I think it should be redefined in false
> when starting logical replication.

In logical replication, however, the process exits after
streamingDoneReceiving is set to true (this happens when sending the
PqMsg_CopyDone message from libpqrcv_endstreaming), so the issue will
not happen in logical replication.
Could you share the client you're using(if it can be shared), along
with the steps you are following when encountering the issue? This
will help us better understand the scenario and potentially create a
test case to reproduce the issue, or at least validate if setting
'streamingDoneReceiving' to false is sufficient.

Regards,
Vignesh