"hehaochen@hotmail.com" <hehaochen@hotmail.com> writes:
> The default is enable_bitmapscan on. However, TPC-H.query17 get slower running on my NVMe SSD (WD SN850) after
switchingon the parameter: latency drop from 9secs to 16secs. During a B-tree Index Scan, bitmapscan optimization
convertsrandom I/O into sequential. However, many users use SSDs rather than HDDs. But they may not know the trick. Is
therea 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