"hehaochen@xxxxxxxxxxx" <hehaochen@xxxxxxxxxxx> 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
