Re: ATSimpleRecursion() and inheritance foreign parents

On 2015/04/28 15:17, Amit Langote wrote:
> The code at the beginning of ATSimpleRecursion() looks like -
>
> /*
> * Propagate to children if desired. Non-table relations never have
> * children, so no need to search in that case.
> */
> if (recurse && rel->rd_rel->relkind == RELKIND_RELATION)
>
> Not sure if it's great idea, but now that foreign tables can also have
> children, should above be changed to take that into account?

Yeah, I think we should now allow the recursion for inheritance parents
that are foreign tables as well. Attached is a patch for that.

> so even foreign inheritance parents expand for
> various ALTER TABLE actions like adding a column though that is not a
> meaningful operation on foreign tables anyway.
>
> An example,
> postgres=# alter foreign table fparent alter a type char;
> ALTER FOREIGN TABLE
>
> postgres=# select * from fparent;
> ERROR: attribute "a" of relation "fchild1" does not match parent's type
>
> Above error, AIUI, is hit much before it is determined that fparent is a
> foreign table, whereas the following is FDW-specific (waiting to happen) error,
>
> postgres=# alter foreign table fparent add b char;
> ALTER FOREIGN TABLE
>
> postgres=# SELECT * FROM fparent;
> ERROR: column "b" does not exist
> CONTEXT: Remote SQL command: SELECT a, b FROM public.parent
>
> Not sure if the first case could be considered s a bug as foreign tables are
> pretty lax in these regards anyway.

I think the first case would be a bug caused by ATSimpleRecursion() that
doesn't allow the recursion. But I don't think the second case is a
bug. As described in the notes in the reference page on ALTER FOREIGN
TABLE, I think it should be the user's responsibility to ensure that the
foreign table definition matches the reality.

Best regards,
Etsuro Fujita