server: add GRPC debug log when set a Env var (pingcap#14140)

Author: lysu

tidb-server/main.go

@@ -17,6 +17,7 @@ import (
 	"context"
 	"flag"
 	"fmt"
+	"io/ioutil"
 	"os"
 	"runtime"
 	"strconv"
@@ -63,6 +64,7 @@ import (
 	"github.com/struCoder/pidusage"
 	"go.uber.org/automaxprocs/maxprocs"
 	"go.uber.org/zap"
+	"google.golang.org/grpc/grpclog"
 )
 
 // Flag Names
@@ -588,6 +590,12 @@ func setupLog() {
 	nopLog := func(string, ...interface{}) {}
 	_, err = maxprocs.Set(maxprocs.Logger(nopLog))
 	terror.MustNil(err)
+
+	if len(os.Getenv("GRPC_DEBUG")) > 0 {
+		grpclog.SetLoggerV2(grpclog.NewLoggerV2WithVerbosity(os.Stderr, os.Stderr, os.Stderr, 999))
+	} else {
+		grpclog.SetLoggerV2(grpclog.NewLoggerV2(ioutil.Discard, ioutil.Discard, os.Stderr))
+	}
 }
 
 func printInfo() {