Re: Support logical replication of DDLs

On Mon, May 9, 2022 at 12:46 PM Bharath Rupireddy
<bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
>
> On Sun, May 8, 2022 at 12:39 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> >
> > On Sat, May 7, 2022 at 9:38 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > > On Fri, May 6, 2022 at 10:21 PM Zheng Li <zhengli10(at)gmail(dot)com> wrote:
> > > >
> > > > > Attached is a set of two patches as an attempt to evaluate this approach.
> > > > >
> > > >
> > > > Thanks for exploring this direction.
> > > >
> > > > I read the deparsing thread and your patch. Here is my thought:
> > > > 1. The main concern on maintainability of the deparsing code still
> > > > applies if we want to adapt it for DDL replication.
> > > >
> > >
> > > I agree that it adds to our maintainability effort, like every time we
> > > enhance any DDL or add a new DDL that needs to be replicated, we
> > > probably need to change the deparsing code. But OTOH this approach
> > > seems to provide better flexibility. So, in the long run, maybe the
> > > effort is worthwhile. I am not completely sure at this stage which
> > > approach is better but I thought it is worth evaluating this approach
> > > as Alvaro and Robert seem to prefer this idea.
> >
> > +1, IMHO with deparsing logic it would be easy to handle the mixed DDL
> > commands like ALTER TABLE REWRITE. But the only thing is that we will
> > have to write the deparsing code for all the utility commands so there
> > will be a huge amount of new code to maintain.
>
> I haven't gone through the entire thread, just trying to understand
> the need of deparsing logic
>

That provided more flexibility, for example, see [1]. We can do things
like identifying the right schema for an object in a way that all
plugins don't need to do specific handling. I think the point Dilip is
highlighting about table rewrite is explained in the email [2]. The
point is that sometimes we can't replay the DDL statement as it is on
the subscriber and deparsing might help in some of those cases even if
not all. At this stage, we are just evaluating both approaches.

[1] - https://www.postgresql.org/message-id/202204081134.6tcmf5cxl3sz%40alvherre.pgsql
[2] - https://www.postgresql.org/message-id/3c646317-df34-4cb3-9365-14abeada6587%40www.fastmail.com

--
With Regards,
Amit Kapila.