Re: row filtering for logical replication

On Wed, Dec 15, 2021 at 5:25 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> > "If a subscriber is a pre-15 version, the initial table
> > synchronization won't use row filters even if they are defined in the
> > publisher."
> >
> > Won't this lead to data inconsistencies or errors that otherwise
> > wouldn't happen?
> >
>
> How? The subscribers will get all the initial data.
>

But couldn't getting all the initial data (i.e. not filtering) break
the rules used by the old/new row processing (see v46-0003 patch)?
Those rules effectively assume rows have been previously published
with filtering.
So, for example, for the following case for UPDATE:
    old-row (no match)    new row (match)  -> INSERT
the old-row check (no match) infers that the old row was never
published, but that row could in fact have been in the initial
unfiltered rows, so in that case an INSERT gets erroneously published
instead of an UPDATE, doesn't it?

> > Should such subscriptions be allowed?
> >
>
> I am not sure what you have in mind here? How can we change the
> already released code pre-15 for this new feature?
>

I was thinking such subscription requests could be rejected by the
server, based on the subscriber version and whether the publications
use filtering etc.


Regards,
Greg Nancarrow
Fujitsu Australia