Stability improvement

[yilongrong]

Feature Request

Describe the feature you'd like:
Stability improvement:
Region physical isolation: splitting, merging, and scheduling require scanning keys to achieve performance cost
Indistinguishable MVCC: read and write amplification, lower performance, GC will bring performance jitter
Compaction: performance jitter
Hotspots: Reduce the impact of hotspots on the system (barrel effect, our current barrel short board is too low)
Fault isolation: The breakdown of a component should theoretically not affect the services of the entire cluster (such as PD switching Leader, which will cause QPS to fall temporarily)

Describe alternatives you've considered:

Stability improvement

https://asktug.com/t/topic/34614/24

[scsldb]

New issue has been suggested, see #18005