Re: Obsolete comment in postgres_fdw.c

On 2016/03/14 16:42, Ashutosh Bapat wrote:
> On Mon, Mar 14, 2016 at 9:05 AM, Etsuro Fujita
> <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp <mailto:fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>> wrote:

> Here is the comments for foreign_join_ok in postgres_fdw.c:
>
> /*
> * Assess whether the join between inner and outer relations can be
> pushed down
> * to the foreign server. As a side effect, save information we obtain
> in this
> * function to PgFdwRelationInfo passed in.
> *
> * Joins that satisfy conditions below are safe to push down.
> *
> * 1) Join type is INNER or OUTER (one of LEFT/RIGHT/FULL)
> * 2) Both outer and inner portions are safe to push-down
> * 3) All foreign tables in the join belong to the same foreign server
> and use
> * the same user mapping.
> * 4) All join conditions are safe to push down
> * 5) No relation has local filter (this can be relaxed for INNER JOIN,
> if we
> * can move unpushable clauses upwards in the join tree).
> */
>
> The condition 3 is now checked by the core, so I'd like to remove that
> condition from the above comments.

> It was left there intentionally to document all the conditions in one
> place (some from the core and some from the FDW itself), for a ready
> reference. In case tomorrow core thinks that matching user mapping is
> not required, postgres_fdw would still require it to be incorporated.

Thank you for the explanation! I understand the reason, but that seems
confusing to me.

> In addition, I'd like to update some related comments in
> src/include/nodes/relation.h and src/backend/optimizer/path/joinpath.c.
>
>
> Those look fine. Sorry for missing those in the commit and thanks for
> providing a patch for the same.

No problem.

Best regards,
Etsuro Fujita