Re: change the default value of enable_bitmapscan to off

"hehaochen(at)hotmail(dot)com" <hehaochen(at)hotmail(dot)com> writes:
> 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?

Use ALTER SYSTEM SET, or edit postgresql.conf:

https://www.postgresql.org/docs/current/config-setting.html

Note that changing planner parameters on the basis of a single
query getting slower is a classic beginner error. You need
to think about the totality of the installation's workload.

regards, tom lane