Support TiFlash's write hotspot scheduling

[HunDunDM]

Feature Request

Describe your feature request related problem

Currently, hot-region-scheduler cannot take effect on TiFlash. The reason is that it relies on the statistical data reported by StoreHeartbeat to determine the direction of scheduling, and the statistical data reported by RegionHeartbeat to determine the Region Peer of the scheduling. Now the statistics in TiFlash's StoreHeartbeat are all 0, so no scheduling can be generated. If a write hotspot appears on TiFlash, it will cause performance degradation.

Describe the feature you'd like

• Support TiFlash's write hotspot scheduling

Describe alternatives you've considered

• TiFlash supports reporting correct statistics in StoreHeartbeat.

Teachability, Documentation, Adoption, Migration Strategy

• Go

[HunDunDM]

related #3261

[rleungx]

Can we close it? @HunDunDM