Re: change the default value of enable_bitmapscan to off

[Pavel Stehule <pavel.stehule@xxxxxxxxx>]

Hi

so 14. 1. 2023 v 15:51 odesílatel hehaochen@xxxxxxxxxxx <hehaochen@xxxxxxxxxxx> 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!