Re: Hybrid Hash/Nested Loop joins and caching results from subplans
| От | Andy Fan |
|---|---|
| Тема | Re: Hybrid Hash/Nested Loop joins and caching results from subplans |
| Дата | |
| Msg-id | CAKU4AWrP9Ga_Am3KtByWuia3ZDiKKV+1Xa1oXoS-==Rbi1gAsg@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Hybrid Hash/Nested Loop joins and caching results from subplans (David Rowley <dgrowleyml@gmail.com>) |
| Ответы |
Re: Hybrid Hash/Nested Loop joins and caching results from subplans
|
| Список | pgsql-hackers |
Thanks for running those tests. I had a quick look at the results and
I think to say that all 4 are better is not quite right. One is
actually a tiny bit slower and one is only faster due to a plan
change.
Yes.. Thanks for pointing it out.
Q18 uses a result cache for 2 x nested loop joins and has a 0% hit
ratio. The execution time is reduced to 91% of the original time only
because the planner uses a different plan, which just happens to be
faster by chance.
Q20 uses a result cache for the subplan and has a 0% hit ratio. The
execution time is 100.27% of the original time. There are 8620 cache
misses.
Looks the case here is some statistics issue or cost model issue. I'd
like to check more about that. But before that, I upload the steps[1] I used
in case you want to reproduce it locally.
Best Regards
Andy Fan
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