Re: postgres_fdw bug in 9.6

On Wed, Jan 18, 2017 at 8:18 AM, Etsuro Fujita
<fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)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