RE: Improve pg_sync_replication_slots() to wait for primary to advance

On Tuesday, February 10, 2026 5:34 PM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> Thanks for the patch.
>
> + * Note that we do not wait and retry if the local slot has been invalidated.
> + * In such cases, the corresponding remote slot on the primary is
> + likely
> + * invalidated as well. Even if only the local slot is invalidated,
> + simply
> + * retrying synchronization won't suffice, as it requires further user
> + actions
> + * to verify the server configuration, drop the invalidated slot.
>
> On thinking more, I realized that if the local slot is invalidated alone while the
> remote-slot is not, we do not wait for the user to drop such an invalidated
> slot. Instead slot-sync will drop it internally. See comments atop
> drop_local_obsolete_slots(). This makes me wonder whether such a case,
> where only the local slot is invalidated, should also set slotsync_pending =
> true, since there is a good chance it will get synchronized in subsequent runs.
> OTOH, if we do not wait for such a slot, we could end up in a situation where
> the slot (remote one) is valid pre-failover but is invalid (synced one) post-
> failover, even after running the API immediately before switchover. Thoughts?

I agree that it makes sense to retry when only the local slot is invalidated.

Here is the updated patch.

Best Regards,
Hou zj