Re: Add a hook for handling logical decoding messages on subscribers.

On Sat, Oct 31, 2026 at 6:05 PM Zhijie Hou <houzhijie22(at)gmail(dot)com> wrote:
>
> On Sat, Oct 31, 2026 at 06:34 AM Masahiko Sawada wrote:
> >
> > It seems to me worth adding a check for tablesync workers since both
> > the apply workers and the tablesync workers call
> > walrcv_startstreaming() and it would prevent mistakes by future
> > changes.
> >
> > I've attached the updated patch.
>
> While reviewing how transactional logical messages interact with
> subtransaction aborts, I noticed an issue with streamed transactions. In
> non-streaming mode, it works as expected (i.e., the message is not
> applied if the subtransaction is aborted). However, in streaming mode,
> if a transactional message is emitted in a subtransaction that is later
> aborted, the STREAM ABORT message does not discard or roll back that
> logical message, so it still gets applied in both streaming=on and
> streaming=parallel modes.
>
> I think the reason is that ReorderBufferApplyMessage() passes the
> top-level txn rather than change->txn to rb->stream_message(), so
> logical decoding always sends the top-level XID instead of the
> subtransaction XID when outputting a streamed message. Thus the apply
> worker cannot associate the message with the subtransaction and cannot
> roll it back properly.
>
> Strictly speaking, this is an existing issue, but it becomes more
> visible once subscribers can handle logical messages via this hook. So
> it may be worth considering whether to fix it along with this patch or
> separately.
>

Right, it didn't have any impact till now for native replication as we
were just ignoring these messages on subscribers. I think this could
have impacted output-plugins if they used this functionality. I think
we can fix this separately but it is better to fix it before this
patch as this patch can expose a hidden issue.

--
With Regards,
Amit Kapila.