On 2015/10/20 13:11, Etsuro Fujita wrote:
On 2015/10/20 5:34, Robert Haas wrote:
On Mon, Oct 19, 2015 at 3:45 AM, Etsuro Fujita
<fujita.ets...@lab.ntt.co.jp> wrote:
As Tom mentioned, just recomputing the original join tuple is not good
enough. We would need to rejoin the test tuples for the baserels
even if
ROW_MARK_COPY is in use. Consider:
A=# BEGIN;
A=# UPDATE t SET a = a + 1 WHERE b = 1;
B=# SELECT * from t, ft1, ft2
WHERE t.a = ft1.a AND t.b = ft2.b AND ft1.c = ft2.c FOR UPDATE;
A=# COMMIT;
where the plan for the SELECT FOR UPDATE is
LockRows
-> Nested Loop
-> Seq Scan on t
-> Foreign Scan on <ft1, ft2>
Remote SQL: SELECT * FROM ft1 JOIN ft2 WHERE ft1.c = ft2.c
AND ft1.a
= $1 AND ft2.b = $2
If an EPQ recheck is invoked by the A's UPDATE, just recomputing the
original join tuple from the whole-row image that you proposed would
output
an incorrect result in the EQP recheck since the value a in the updated
version of a to-be-joined tuple in t would no longer match the value
ft1.a
extracted from the whole-row image if the A's UPDATE has committed
successfully. So I think we would need to rejoin the tuples
populated from
the whole-row images for the baserels ft1 and ft2, by executing the
secondary plan with the new parameter values for a and b.
No. You just need to populate fdw_recheck_quals correctly, same as
for the scan case.
Yeah, I think we can probably do that for the case where a pushed-down
join clause is an inner-join one, but I'm not sure that we can do that
for the case where that clause is an outer-join one. Maybe I'm missing
something, though.
As I said yesterday, that opinion of me is completely wrong. Sorry for
the incorrectness. Let me explain a little bit more. I still think
that even if ROW_MARK_COPY is in use, we would need to locally rejoin
the tuples populated from the whole-row images for the foreign tables
involved in a remote join, using a secondary plan. Consider eg,
SELECT localtab.*, ft2 from localtab, ft1, ft2
WHERE ft1.x = ft2.x AND ft1.y = localtab.y FOR UPDATE
In this case, since the output of the foreign join would not include any
ft1 columns, I don't think we could do the same thing as for the scan
case, even if populating fdw_recheck_quals correctly. And I think we
would need to rejoin the tuples, using a local join execution plan,
which would have the parameterization for the to-be-pushed-down clause
ft1.y = localtab.y. I'm still missing something, though.
Best regards,
Etsuro Fujita
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