Re: [PERFORM] Query with no result set, really really slow addingORBDER BY / LIMIT clause

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От Marco Renzi
Тема Re: [PERFORM] Query with no result set, really really slow addingORBDER BY / LIMIT clause
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Msg-id CAHmtSMZ1+s4voZidJdF92uVQgY+XOMe3THQo9p5XFpb4HwzXNA@mail.gmail.com
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Ответ на Re: [PERFORM] Query with no result set, really really slow addingORBDER BY / LIMIT clause  (Pavel Stehule <pavel.stehule@gmail.com>)
Ответы Re: [PERFORM] Query with no result set, really really slow addingORBDER BY / LIMIT clause  (Pavel Stehule <pavel.stehule@gmail.com>)
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I am thinking so limit 10000 should be ok. Too big number can be messy for optimizer similarly like too small number.

The planner is driven by statistics - and the statistics are not perfect - usually it is working on 80% - like weather forecasting.

Usually it is working, but sometimes not.

Regards

Pavel
 


Thanks Pavel, i almost found two solutions at the end:
One is to use an inner limit as you said, and the other, when you just know what the filter is,
is to try to join with SELECTS that have to be executed first from the planner.

Eg
SELECT  fase.id
FROM            tipofase
JOIN       fase
ON         (fase.tipofase = (SELECT tipofase.id FROM tipofase WHERE tipofase.agendafrontoffice = true))

ORDER BY        fase.id DESC   limit 10 offset 0

Thanks for the help

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OCP - Oracle Certified Mysql 5 Developer

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