tikv: update default settings of server.grpc-concurrency and server.grpc-raft-conn-num.

tikv-configuration-file.md

@@ -151,7 +151,10 @@ This document only describes the parameters that are not included in command-lin
 ### `grpc-concurrency`
 
 + The number of gRPC worker threads. When you modify the size of the gRPC thread pool, refer to [Performance tuning for TiKV thread pools](/tune-tikv-thread-performance.md#performance-tuning-for-tikv-thread-pools).
-+ Default value: `5`
++ Default value: `grpc-raft-conn-num * 3 + 2` (starting from v8.5.4 and v9.0.0), which is calculated based on the value of [`grpc-raft-conn-num`](#grpc-raft-conn-num). In v8.5.3 and earlier versions, the default value is `5`.
+
+    + For example, when the number of CPU cores is 8, the default value of `grpc-raft-conn-num` is 1. Accordingly, the default value of `grpc-concurrency` is `1 * 3 + 2 = 5`.
+
 + Minimum value: `1`
 
 ### `grpc-concurrent-stream`
@@ -169,7 +172,7 @@ This document only describes the parameters that are not included in command-lin
 ### `grpc-raft-conn-num`
 
 + The maximum number of connections between TiKV nodes for Raft communication
-+ Default value: `1`
++ Default value: `MAX(1, MIN(4, CPU cores / 8))` (starting from v8.5.4 and v9.0.0), where `MIN(4, CPU cores / 8)` indicates that when the number of CPU cores is greater than or equal to 32, the default maximum number of connections is 4. In v8.5.3 and earlier versions, the default value is 1.
 + Minimum value: `1`
 
 ### `max-grpc-send-msg-len`

tune-tikv-thread-performance.md

@@ -43,7 +43,7 @@ Starting from TiKV v5.0, all read requests use the unified thread pool for queri
 
 * The gRPC thread pool.
 
-    The default size (configured by `server.grpc-concurrency`) of the gRPC thread pool is `5`. This thread pool has almost no computing overhead and is mainly responsible for network I/O and deserialization requests, so generally you do not need to adjust the default configuration.
+    Starting from v8.5.4 and v9.0.0, the default size of the gRPC thread pool (configured by `server.grpc-concurrency`) is changed from a fixed value of `5` to an adaptive value calculated based on the number of CPU cores. For the detailed calculation formula, see [`server.grpc-concurrency`](/tikv-configuration-file.md#grpc-concurrency). This thread pool has almost no computing overhead and is mainly responsible for network I/O and deserialization requests, so generally you do not need to adjust the default configuration.
 
     - If the machine deployed with TiKV has a small number (less than or equal to 8) of CPU cores, consider setting the `server.grpc-concurrency` configuration item to `2`.
     - If the machine deployed with TiKV has very high configuration, TiKV undertakes a large number of read and write requests, and the value of `gRPC poll CPU` that monitors Thread CPU on Grafana exceeds 80% of `server.grpc-concurrency`, then consider increasing the value of `server.grpc-concurrency` to keep the thread pool usage rate below 80% (that is, the metric on Grafana is lower than `80% * server.grpc-concurrency`).