Re: postgres_fdw bug in 9.6

On Wed, Jan 18, 2017 at 8:18 AM, Etsuro Fujita
<fujita.etsuro@lab.ntt.co.jp> wrote:
> On 2017/01/16 11:38, Etsuro Fujita wrote:
>>
>> On 2017/01/14 6:39, Jeff Janes wrote:
>>>
>>> I do get a compiler warning:
>>>
>>> foreign.c: In function 'CreateLocalJoinPath':
>>> foreign.c:832: warning: implicit declaration of function
>>> 'pathkeys_contained_in'
>
>
>> Will fix.
>
>
> Done.  Attached is the new version.  I also adjusted the code a bit further.

With this patch there are multiple cases, where CreateLocalJoinPath()
would return NULL and hence postgres_fdw would not push a join down
for example
                /*
                 * (1) if either cheapest-total path is parameterized by the
                 * other rel, we can't generate a hashjoin/mergejoin path, and
                 * (2) proposed hashjoin/mergejoin path is still parameterized
                 * (ie, the required_outer set calculated by
                 * calc_non_nestloop_required_outer isn't NULL), it's not what
                 * we want; which means that both the cheapest-total paths
                 * should be unparameterized.
                 */
                if (outer_path->param_info || inner_path->param_info)
                    return NULL;
or
                /*
                 * If the cheapest-total outer path is parameterized by the
                 * inner rel, we can't generate a nestloop path.  (There's no
                 * use looking for alternative outer paths, since it should
                 * already be the least-parameterized available path.)
                 */
                if (PATH_PARAM_BY_REL(outer_path, innerrel))
                    return NULL;
                /* If proposed path is still parameterized, don't return it. */
                required_outer = calc_nestloop_required_outer(outer_path,
                                                              inner_path);
                if (required_outer)
                {
                    bms_free(required_outer);
                    return NULL;
                }

Am I right?

The earlier version of this function GetExistingLocalJoinPath() used
to return a local path in those cases and hence postgres_fdw was able
to push down corresponding queries. So, we are introducing a
performance regression. We need to plug those holes.

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