Re: BUG #15233: Error in estimation leads to very bad parralel planin simple 2 table join.
| От | Maxim Boguk |
|---|---|
| Тема | Re: BUG #15233: Error in estimation leads to very bad parralel planin simple 2 table join. |
| Дата | |
| Msg-id | CAK-MWwRh=J70OTJYtct-j=RV2BmPtq4bhMzgPtwN4Vc0ygBcxQ@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: BUG #15233: Error in estimation leads to very bad parralel planin simple 2 table join. (Amit Kapila <amit.kapila16@gmail.com>) |
| Список | pgsql-bugs |
Is it because you have not performed Analyze on the 'area' or is it> Planning time: 2.953 ms
> Execution time: 2084537.882 ms
>
> Problem with estimation of selectivity
> -> Seq Scan on area a (cost=0.00..265.70 rows=1 width=106) (actual
> time=0.669..1.756 rows=23 loops=1)
>Filter: ((path)::text ~~ '%.1806.%'::text)
> leads to very dangerous idea to perform nested loop with very heavy parallel
> plan inside.
>
something else due to which there is such a deviation in estimation?
Hi,
I don't think there is good way estimate selectivity of
Filter: ((path)::text ~~ '%.1806.%'::text) But problem that there huge difference in real plan cost with exactly 1 row vs 2 or more rows estimated. Problem still exists without parallel plan involved, where is leads to 23 seq scan over table with 100M rows :(.
--
Maxim Boguk
Senior Postgresql DBA
http://dataegret.com/
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Skype: maxim.boguk
"Доктор, вы мне советовали так не делать, но почему мне по-прежнему больно когда я так делаю ещё раз?"
Senior Postgresql DBA
http://dataegret.com/
Phone RU: +7 985 433 0000
Phone UA: +380 99 143 0000
Phone AU: +61 45 218 5678
LinkedIn: http://www.linkedin.com/pub/maksym-boguk/80/b99/b1b
Skype: maxim.boguk
"Доктор, вы мне советовали так не делать, но почему мне по-прежнему больно когда я так делаю ещё раз?"
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