Re: Slow Count-Distinct Query
| От | Shaun Thomas |
|---|---|
| Тема | Re: Slow Count-Distinct Query |
| Дата | |
| Msg-id | 0683F5F5A5C7FE419A752A034B4A0B979785A92E@sswchi5pmbx2.peak6.net обсуждение исходный текст |
| Ответ на | Slow Count-Distinct Query (Christopher Jackson <crjackso@gmail.com>) |
| Список | pgsql-performance |
> tl;dr - How can I speed up my count-distinct query? You can't. Doing a count(distinct x) is much different than a count(1), which can simply scan available indexes. To build a distinct,it has to construct an in-memory hash of every valid email, and count the distinct values therein. This will prettymuch never be fast, especially with 2M rows involved. I could be wrong about this, and the back-end folks might have a different answer, but I wouldn't hold my breath. -- Shaun Thomas OptionsHouse | 141 W. Jackson Blvd | Suite 400 | Chicago IL, 60604 312-676-8870 sthomas@optionshouse.com ______________________________________________ See http://www.peak6.com/email_disclaimer/ for terms and conditions related to this email
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