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

On Mon, Nov 2, 2026 at 4:47 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> 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.

Agreed that we should fix it before this patch.

The Hou's patch looks good. I prefer to apply it to only master as
external output plugin might require changes similar to what the patch
does for test_decoding.

And thank you for the 0002 patch. I'll include it in the next version patch.

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com