Re: pgsql: postgres_fdw: Inherit the local transaction's access/deferrable

On Sun, Feb 15, 2026 at 5:40 PM Etsuro Fujita <etsuro.fujita@gmail.com> wrote:
> On Wed, Jun 4, 2025 at 1:15 PM Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
> > I agree this could be considered a fix if the new behavior has been
> > clearly explained in the documentation from before or based on
> > standards like SQL/MED. But if that's not the case, it seems more
> > like a behavior change. In that case, I think it should wait for v19
> > and be applied only after reaching consensus. Some systems might
> > rely on the previous behavior.
> >
> > By the way, if a read-only transaction on the local server is meant
> > to block all write operations on the remote server, this patch alone
> > might not be sufficient, for example, that read-only transaction can
> > invoke a login trigger on the remote server and it could still
> > perform writes.
>
> This patch 1) modifies postgres_fdw so that it opens remote
> transactions in read-only mode if the corresponding local transaction
> is read-only, as noted in the documentation, but 2) keeps the existing
> behavior of login triggers that they can write even if the invoking
> transaction is read-only.  So declaring a transaction as read-only on
> the local side doesn't mean it blocks all write operations on the
> remote side; it still allows login triggers invoked on the remote side
> to write.  Considering typical use-cases of such triggers, this seems
> reasonable to me.  I think it might be a good idea to add a note about
> it to the documentation, though.
>
> I'd like to re-propose this patch for v19, as mentioned in this thread.

I posted a new version of the patch to the -hackers mailing list [1],
which includes the note mentioned above.  It would be great if I got
feedback from you.

Best regards,
Etsuro Fujita

[1] https://www.postgresql.org/message-id/CAPmGK14ZTHRGPprEhzEe2TJxaCcjNVeWw6tue_gqp%3D9DzqYnMA%40mail.gmail.com