Re: Unnecessary lateral dependencies implied by PHVs
| От | Andy Fan |
|---|---|
| Тема | Re: Unnecessary lateral dependencies implied by PHVs |
| Дата | |
| Msg-id | CAKU4AWoEqy3kGWWYgNbNDe=9DyuA54Jb=6bSLWk3PuF8rwsWqg@mail.gmail.com обсуждение исходный текст |
| Ответ на | Unnecessary lateral dependencies implied by PHVs (Richard Guo <guofenglinux@gmail.com>) |
| Ответы |
Re: Unnecessary lateral dependencies implied by PHVs
|
| Список | pgsql-hackers |
Hi Richard:
On Mon, Oct 10, 2022 at 10:35 AM Richard Guo <guofenglinux@gmail.com> wrote:
... I'm asking because
PHVs may imply lateral dependencies which may make us have to use
nestloop join.
I thought lateral join imply nestloop join, am I missing something? Here is my simple
testing.
postgres=# explain (costs off) select * from r1 join lateral (select r1.a from r2) on true;
QUERY PLAN
----------------------------
Nested Loop
-> Seq Scan on r1
-> Materialize
-> Seq Scan on r2
(4 rows)
Time: 0.349 ms
postgres=# set enable_nestloop to off;
SET
Time: 0.123 ms
QUERY PLAN
----------------------------
Nested Loop
-> Seq Scan on r1
-> Materialize
-> Seq Scan on r2
(4 rows)
Time: 0.349 ms
postgres=# set enable_nestloop to off;
SET
Time: 0.123 ms
postgres=# explain (costs off) select * from r1 join lateral (select r1.a from r2) on true;
QUERY PLAN
----------------------------
Nested Loop
-> Seq Scan on r1
-> Materialize
-> Seq Scan on r2
(4 rows)
Best Regards
Andy Fan
В списке pgsql-hackers по дате отправления: