Add gRPC local subchannel support for tikv client.

Signed-off-by: yulai.li <[email protected]>

Author: blacktear23

tikv-client-common/src/security.rs

@@ -4,6 +4,7 @@ use crate::Result;
 use grpcio::{Channel, ChannelBuilder, ChannelCredentialsBuilder, Environment};
 use regex::Regex;
 use std::{
+    ffi::CString,
     fs::File,
     io::Read,
     path::{Path, PathBuf},
@@ -76,9 +77,12 @@ impl SecurityManager {
 
         let addr = SCHEME_REG.replace(addr, "");
 
+        // Set grpc.use_local_subchannel_pool will ensure every TiKV client instance can has it's own
+        // connection to TiKV server.
         let cb = ChannelBuilder::new(env)
             .keepalive_time(Duration::from_secs(10))
-            .keepalive_timeout(Duration::from_secs(3));
+            .keepalive_timeout(Duration::from_secs(3))
+            .raw_cfg_int(CString::new("grpc.use_local_subchannel_pool").unwrap(), 1);
 
         let channel = if self.ca.is_empty() {
             cb.connect(&addr)