Re: row filtering for logical replication

On Wed, Jul 14, 2021 at 3:58 PM Tomas Vondra
<tomas(dot)vondra(at)enterprisedb(dot)com> wrote:
>
> On 7/14/21 7:39 AM, Amit Kapila wrote:
> > On Wed, Jul 14, 2021 at 6:28 AM Euler Taveira <euler(at)eulerto(dot)com> wrote:
> >>
> >> On Tue, Jul 13, 2021, at 6:06 PM, Alvaro Herrera wrote:
> >>
> >> 1. if you use REPLICA IDENTITY FULL, then the expressions would work
> >> even if they use any other column with DELETE. Maybe it would be
> >> reasonable to test for this in the code and raise an error if the
> >> expression requires a column that's not part of the replica identity.
> >> (But that could be relaxed if the publication does not publish
> >> updates/deletes.)
> >>
> >
> > +1.
> >
> >> I thought about it but came to the conclusion that it doesn't worth it. Even
> >> with REPLICA IDENTITY FULL expression evaluates to false if the column allows
> >> NULL values. Besides that REPLICA IDENTITY is changed via another DDL (ALTER
> >> TABLE) and you have to make sure you don't allow changing REPLICA IDENTITY
> >> because some row filter uses the column you want to remove from it.
> >>
> >
> > Yeah, that is required but is it not feasible to do so?
> >
> >> 2. For UPDATE, does the expression apply to the old tuple or to the new
> >> tuple? You say it's the new tuple, but from the user point of view I
> >> think it would make more sense that it would apply to the old tuple.
> >> (Of course, if you're thinking that the R.I. is the PK and the PK is
> >> never changed, then you don't really care which one it is, but I bet
> >> that some people would not like that assumption.)
> >>
> >> New tuple. The main reason is that new tuple is always there for UPDATEs.
> >>
> >
> > I am not sure if that is a very good reason to use a new tuple.
> >
>
> True. Perhaps we should look at other places with similar concept of
> WHERE conditions and old/new rows, and try to be consistent with those?
>
> I can think of:
>
> 1) updatable views with CHECK option
>
> 2) row-level security
>
> 3) triggers
>
> Is there some reasonable rule which of the old/new tuples (or both) to
> use for the WHERE condition? Or maybe it'd be handy to allow referencing
> OLD/NEW as in triggers?
>

I think apart from the above, it might be good if we can find what
some other databases does in this regard?

--
With Regards,
Amit Kapila.