Re: row filtering for logical replication

On Fri, Nov 23, 2018 at 3:55 PM Petr Jelinek <petr.jelinek@2ndquadrant.com> wrote:
>
> On 23/11/2018 17:15, Euler Taveira wrote:
> > Em qui, 22 de nov de 2018 às 20:03, Petr Jelinek
> > <petr.jelinek@2ndquadrant.com> escreveu:
> >> Firstly, I am not sure if it's wise to allow UDFs in the filter clause
> >> for the table. The reason for that is that we can't record all necessary
> >> dependencies there because the functions are black box for parser. That
> >> means if somebody drops object that an UDF used in replication filter
> >> depends on, that function will start failing. But unlike for user
> >> sessions it will start failing during decoding (well processing in
> >> output plugin). And that's not recoverable by reading the missing
> >> object, the only way to get out of that is either to move slot forward
> >> which means losing part of replication stream and need for manual resync
> >> or full rebuild of replication. Neither of which are good IMHO.
> >>
> > It is a foot gun but there are several ways to do bad things in
> > postgres. CREATE PUBLICATION is restricted to superusers and role with
> > CREATE privilege in current database. AFAICS a role with CREATE
> > privilege cannot drop objects whose owner is not himself. I wouldn't
> > like to disallow UDFs in row filtering expressions just because
> > someone doesn't set permissions correctly. Do you have any other case
> > in mind?
>
> I don't think this has anything to do with security. Stupid example:
>
> user1: CREATE EXTENSION citext;
>
> user2: CREATE FUNCTION myfilter(col1 text, col2 text) returns boolean
> language plpgsql as
> $$BEGIN
> RETURN col1::citext = col2::citext;
> END;$$
>
> user2: ALTER PUBLICATION mypub ADD TABLE mytab WHERE (myfilter(a,b));
>
> [... replication happening ...]
>
> user1: DROP EXTENSION citext;
>
> And now replication is broken and unrecoverable without data loss.
> Recreating extension will not help because the changes happening in
> meantime will not see it in the historical snapshot.
>
> I don't think it's okay to do completely nothing about this.
>

If carefully documented I see no problem with it... we already have an analogous problem with functional indexes.

Regards,