Re: [HACKERS] 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
stillparameterized                * (ie, the required_outer set calculated by                *
calc_non_nestloop_required_outerisn't NULL), it's not what                * we want; which means that both the
cheapest-totalpaths                * 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