Re: postgres_fdw join pushdown (was Re: Custom/Foreign-Join-APIs)

On Thu, Feb 4, 2016 at 3:28 PM, Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>
wrote:

> On 2016/02/04 17:58, Etsuro Fujita wrote:
>
>> On 2016/02/04 8:00, Robert Haas wrote:
>>
>>> On Wed, Feb 3, 2016 at 5:56 PM, Robert Haas <robertmhaas(at)gmail(dot)com>
>>> wrote:
>>>
>>>> On Wed, Feb 3, 2016 at 12:08 PM, Ashutosh Bapat
>>>> <ashutosh(dot)bapat(at)enterprisedb(dot)com> wrote:
>>>>
>>>>> PFA patches with naming conventions similar to previous ones.
>>>>> pg_fdw_core_v7.patch: core changes
>>>>> pg_fdw_join_v7.patch: postgres_fdw changes for join pushdown
>>>>> pg_join_pd_v7.patch: combined patch for ease of testing.
>>>>>
>>>>
> One more: I think the following in postgresGetForeignJoinPaths() is a good
> idea, but I think it's okay to just check whether root->rowMarks is
> non-NIL, because that since we have rowmarks for all base relations except
> the target, if we have root->parse->commandType==CMD_DELETE (or
> root->parse->commandType==CMD_UPDATE), then there would be at least one
> non-target base relation in the joinrel, which would have a rowmark.
>
>
Sorry, I am unable to understand it fully. But what you are suggesting that
if there are root->rowMarks, then we are sure that there is at least one
base relation apart from the target, which needs locking rows. Even if we
don't have one, still changes in a row of target relation after it was
scanned, can result in firing EPQ check, which would need the local plan to
be executed, thus even if root->rowMarks is NIL, EPQ check can fire and we
will need alternate local plan.

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