Polish the TiKV Trouble Shooting part. (#15220) (#15547)

Author: ti-chi-bot

Diff for: best-practices/pd-scheduling-best-practices.md

@@ -296,4 +296,8 @@ If a TiKV node fails, PD defaults to setting the corresponding node to the **dow
 
 Practically, if a node failure is considered unrecoverable, you can immediately take it offline. This makes PD replenish replicas soon in another node and reduces the risk of data loss. In contrast, if a node is considered recoverable, but the recovery cannot be done in 30 minutes, you can temporarily adjust `max-store-down-time` to a larger value to avoid unnecessary replenishment of the replicas and resources waste after the timeout.
 
-In TiDB v5.2.0, TiKV introduces the mechanism of slow TiKV node detection. By sampling the requests in TiKV, this mechanism works out a score ranging from 1 to 100. A TiKV node with a score higher than or equal to 80 is marked as slow. You can add [`evict-slow-store-scheduler`](/pd-control.md#scheduler-show--add--remove--pause--resume--config--describe) to detect and schedule slow nodes. If only one TiKV is detected as slow, and the slow score reaches the limit (80 by default), the leader in this node will be evicted (similar to the effect of `evict-leader-scheduler`).
+In TiDB v5.2.0, TiKV introduces the mechanism of slow TiKV node detection. By sampling the requests in TiKV, this mechanism works out a score ranging from 1 to 100. A TiKV node with a score higher than or equal to 80 is marked as slow. You can add [`evict-slow-store-scheduler`](/pd-control.md#scheduler-show--add--remove--pause--resume--config--describe) to detect and schedule slow nodes. If only one TiKV is detected as slow, and the slow score reaches the limit (80 by default), the Leader in this node will be evicted (similar to the effect of `evict-leader-scheduler`).
+
+> **Note:**
+>
+> **Leader eviction** is accomplished by PD sending scheduling requests to TiKV slow nodes and then TiKV executing the received scheduling requests sequentially. Due to factors such as **slow I/O**, slow nodes might experience request accumulation, causing some Leaders to wait until the delayed requests are processed before handling **Leader eviction** requests. This results in an overall extended time for **Leader eviction**. Therefore, when you enable `evict-slow-store-scheduler`, it is recommended to enable [`store-io-pool-size`](/tikv-configuration-file.md#store-io-pool-size-new-in-v530) as well to mitigate this situation.