add scheduling policy within a transaction (#16056)

follower-read.md

@@ -66,4 +66,4 @@ When the follower node processes a read request, it first uses `ReadIndex` of th
 
 Because the Follower Read feature does not affect TiDB's Snapshot Isolation transaction isolation level, TiDB adopts the round-robin strategy to select the follower replica. Currently, for the coprocessor requests, the granularity of the Follower Read load balancing policy is at the connection level. For a TiDB client connected to a specific Region, the selected follower is fixed, and is switched only when it fails or the scheduling policy is adjusted.
 
-However, for the non-coprocessor requests, such as a point query, the granularity of the Follower Read load balancing policy is at the transaction level. For a TiDB transaction on a specific Region, the selected follower is fixed, and is switched only when it fails or the scheduling policy is adjusted.
+However, for the non-coprocessor requests, such as a point query, the granularity of the Follower Read load balancing policy is at the transaction level. For a TiDB transaction on a specific Region, the selected follower is fixed, and is switched only when it fails or the scheduling policy is adjusted. If a transaction contains both point queries and coprocessor requests, the two types of requests are scheduled for reading separately according to the preceding scheduling policy. In this case, even if a coprocessor request and a point query are for the same Region, TiDB processes them as independent events.