Re: pg_dump compatibility level / use create view instead of create table/rule

Hi,

On 2019-10-10 11:20:14 -0400, Tom Lane wrote:
> regression=# create table mytab (f1 int primary key, f2 text);
> CREATE TABLE
> regression=# create view myview as select * from mytab group by f1;
> CREATE VIEW
>
> This situation is problematic for pg_dump because validity of the
> view depends on the existence of mytab's primary key constraint,
> and we don't create primary keys till late in the restore process.
> So it has to break myview into two parts, one to emit during normal
> table/view creation and one to emit after index creation.
>
> With 9.5's pg_dump, what comes out is:
>
> --
> -- Name: myview; Type: TABLE; Schema: public; Owner: postgres
> --
>
> CREATE TABLE public.myview (
> f1 integer,
> f2 text
> );
>
> ALTER TABLE ONLY public.myview REPLICA IDENTITY NOTHING;

Ick.

> The reason we get "REPLICA IDENTITY NOTHING" is that a view's relreplident
> is set to 'n' not 'd', which might not have been a great choice.

Hm, yea. I wonder if we should add a REPLICA_IDENTITY_INVALID or such,
for non relation relkinds? I'm mildly inclined to think that setting it
to REPLICA_IDENTITY_DEFAULT is at least as confusing as
REPLICA_IDENTITY_DEFAULT...

> This is fixed in v10 and up thanks to d8c05aff5. I was hesitant to
> back-patch that at the time, but now that it's survived in the field
> for a couple years, I think a good case could be made for doing so.

+1

> /* pretend view is a plain table and dump it that way */
> viewinfo->relkind = 'r'; /* RELKIND_RELATION */
> viewinfo->relkind = 'r'; /* RELKIND_RELATION */
> + viewinfo->relreplident = 'd'; /* REPLICA_IDENTITY_DEFAULT */
>
> That's mighty ugly but it doesn't seem to carry any particular
> risk.

I also could live with this, given it'd only be in older back-branches.

Greetings,

Andres Freund