On 7/16/20 9:35 PM, Etsuro Fujita wrote:
On Thu, Jul 16, 2020 at 8:56 PM Andrey Lepikhov
<a.lepik...@postgrespro.ru> wrote:
On 7/16/20 9:55 AM, Etsuro Fujita wrote:
On Tue, Jul 14, 2020 at 12:48 AM Alexey Kondratov
<a.kondra...@postgrespro.ru> wrote:
Some real-life test queries show, that all single-node queries aren't
pushed-down to the required node. For example:
SELECT
*
FROM
documents
INNER JOIN users ON documents.user_id = users.id
WHERE
documents.company_id = 5
AND users.company_id = 5;
PWJ cannot be applied
to the join due to the limitation of the PWJ matching logic. See the
discussion started in [1]. I think the patch in [2] would address
this issue as well, though the patch is under review.
I think, discussion [1] is little relevant to the current task. Here we
join not on partition attribute and PWJ can't be used at all.
The main point of the discussion is to determine whether PWJ can be
used for a join between partitioned tables, based on
EquivalenceClasses, not just join clauses created by
build_joinrel_restrictlist(). For the above join, for example, the
patch in [2] would derive a join clause "documents.company_id =
users.company_id" from an EquivalenceClass that recorded the knowledge
"documents.company_id = 5" and "users.company_id = 5", and then the
planner would consider from it that PWJ can be used for the join.
Ok, this patch works and you solved a part of the problem with this
interesting approach.
But you can see that modification of the query:
SELECT * FROM documents, users WHERE documents.company_id = 5 AND
users.company_id = 7;
also can be pushed into node2 and joined there but not.
My point is that we can try to solve the whole problem.
--
regards,
Andrey Lepikhov
Postgres Professional
