# Case Study Background (A)

+ Description of business scenario
  + Cluster topology: 12 TiDB Servers, 5 TiKVs
  + Question time: After 10:00am
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- Cluster version
  - v4.0.2
- Cluster topology
  - 12 tidb, 5 tikv 
- Description of the problem
  - The cluster writes slowly, the tikv CPU is high, and the current duration is high up to min level. Under normal conditions, the duration 99 line is about 4s