On Mon, Jul 29, 2025 at 8:13 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> That is true but I still feel there has to be some mechanism where we
> can catch and give an ERROR to the user, if it doesn't follow the
> same. For example, pg_replication_origin_advance() always allows going
> backwards in terms of LSN which means if one doesn't follow commit
> order, it can lead to breaking the replication as after restart the
> client can ask to start replication from some prior point.
If you have any ideas for safeguards or API changes, I'd be happy to
help implement them or discuss them.
> Can you tell us the use case? Did you also intend to use it for parallel apply, if so, can you also tell at a high
> level, how you are planning to manage origin?
Yes, we use it for parallel apply. We have a custom logical
replication system that applies changes using multiple worker
processes, each with their own database connection.
Our use case requires multiple connections to be able to advance the
same replication origin. We handle this by having a master process
coordinate the workers, where each worker process calls
pg_replication_origin_session_setup with the master's PID as the
second parameter.
We may send operations out of order but we always commit in order, so
there's no chance of creating inconsistencies. There's the chance of
deadlocks, but these can be detected. It's really similar to the
existing parallel apply implementation - the main difference is that
we're applying from jsonl files instead of directly from another
database.
Currently we use a local patch to expose the PID parameter, but having
this upstream would be great. It causes a lot of headaches for us to
use a patched PostgreSQL.
Thanks,
Doruk Yılmaz