Re: change the default value of enable_bitmapscan to off

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От Pavel Stehule
Тема Re: change the default value of enable_bitmapscan to off
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Msg-id CAFj8pRBKy7vWpN0-jxk24UnEiEbqA5-gFzyjbiO9gkHmuw-fig@mail.gmail.com
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Ответ на change the default value of enable_bitmapscan to off  ("hehaochen@hotmail.com" <hehaochen@hotmail.com>)
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Hi


so 14. 1. 2023 v 15:51 odesílatel hehaochen@hotmail.com <hehaochen@hotmail.com> napsal:
The default is enable_bitmapscan on. However, TPC-H.query17 get slower running on my NVMe SSD (WD SN850) after switching on the parameter: latency drop from 9secs to 16secs. During a B-tree Index Scan, bitmapscan optimization converts random I/O into sequential. However, many users use SSDs rather than HDDs. But they may not know the trick. Is there a possibility that can change the default value to off?

I don't think it can be disabled by default.

When you have fast SSD disk, then common setting is decreasing random_page_cost to some value to 2 or maybe 1.5

Regards

Pavel
 

Thanks!

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