Re: Check lateral references within PHVs for memoize cache keys
| От | Richard Guo |
|---|---|
| Тема | Re: Check lateral references within PHVs for memoize cache keys |
| Дата | |
| Msg-id | CAMbWs496+dPCsMdfwwJwz9u1T5vwz08rZxWaTKYxprXw5Neu4Q@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Check lateral references within PHVs for memoize cache keys (David Rowley <dgrowleyml@gmail.com>) |
| Список | pgsql-hackers |
On Tue, Jan 24, 2023 at 10:07 AM David Rowley <dgrowleyml@gmail.com> wrote:
I'm surprised to see that it's only Memoize that ever makes use of
lateral_vars. I'd need a bit more time to process your patch, but one
additional thought I had was that I wonder if the following code is
still needed in nodeMemoize.c
if (bms_nonempty_difference(outerPlan->chgParam, node->keyparamids))
cache_purge_all(node);
Ideally, that would be an Assert failure, but possibly we should
probably still call cache_purge_all(node) after Assert(false) so that
at least we'd not start returning wrong results if we've happened to
miss other cache keys. I thought maybe something like:
Hmm, I think this code is still needed because the parameter contained
in the subplan below a Memoize node may come from parent plan, as in the
test query added in 411137a42.
EXPLAIN (COSTS OFF)
SELECT unique1 FROM tenk1 t0
WHERE unique1 < 3
AND EXISTS (
SELECT 1 FROM tenk1 t1
INNER JOIN tenk1 t2 ON t1.unique1 = t2.hundred
WHERE t0.ten = t1.twenty AND t0.two <> t2.four OFFSET 0);
QUERY PLAN
----------------------------------------------------------------
Index Scan using tenk1_unique1 on tenk1 t0
Index Cond: (unique1 < 3)
Filter: (SubPlan 1)
SubPlan 1
-> Nested Loop
-> Index Scan using tenk1_hundred on tenk1 t2
Filter: (t0.two <> four)
-> Memoize
Cache Key: t2.hundred
Cache Mode: logical
-> Index Scan using tenk1_unique1 on tenk1 t1
Index Cond: (unique1 = t2.hundred)
Filter: (t0.ten = twenty)
(13 rows)
Currently we don't have a way to add Params of uplevel vars to Memoize
cache keys. So I think we still need to call cache_purge_all() each
time uplevel Params change.
Thanks
Richard
in the subplan below a Memoize node may come from parent plan, as in the
test query added in 411137a42.
EXPLAIN (COSTS OFF)
SELECT unique1 FROM tenk1 t0
WHERE unique1 < 3
AND EXISTS (
SELECT 1 FROM tenk1 t1
INNER JOIN tenk1 t2 ON t1.unique1 = t2.hundred
WHERE t0.ten = t1.twenty AND t0.two <> t2.four OFFSET 0);
QUERY PLAN
----------------------------------------------------------------
Index Scan using tenk1_unique1 on tenk1 t0
Index Cond: (unique1 < 3)
Filter: (SubPlan 1)
SubPlan 1
-> Nested Loop
-> Index Scan using tenk1_hundred on tenk1 t2
Filter: (t0.two <> four)
-> Memoize
Cache Key: t2.hundred
Cache Mode: logical
-> Index Scan using tenk1_unique1 on tenk1 t1
Index Cond: (unique1 = t2.hundred)
Filter: (t0.ten = twenty)
(13 rows)
Currently we don't have a way to add Params of uplevel vars to Memoize
cache keys. So I think we still need to call cache_purge_all() each
time uplevel Params change.
Thanks
Richard
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