Thread: Obsolete comment in postgres_fdw.c

Obsolete comment in postgres_fdw.c

From
Etsuro Fujita
Date:
Hi,

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.

In addition, I'd like to update some related comments in
src/include/nodes/relation.h and src/backend/optimizer/path/joinpath.c.

Attached is a patch for that.

Best regards,
Etsuro Fujita

Attachment

Re: Obsolete comment in postgres_fdw.c

From
Ashutosh Bapat
Date:


On Mon, Mar 14, 2016 at 9:05 AM, Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp> wrote:
Hi,

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.
 

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.

--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company

Re: Obsolete comment in postgres_fdw.c

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





Re: Obsolete comment in postgres_fdw.c

From
Robert Haas
Date:
On Mon, Mar 14, 2016 at 4:31 AM, Etsuro Fujita
<fujita.etsuro@lab.ntt.co.jp> wrote:
>> 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.

Agreed.

>>     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.

Committed.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company