From 8a0a06dac9d397cfa337f7c2e1a388412d082b2b Mon Sep 17 00:00:00 2001
From: cbcwestwolf <1004626265@qq.com>
Date: Mon, 20 Jun 2022 20:11:47 +0800
Subject: [PATCH] Change error information

---
 server/server.go                 | 27 +++++----------------------
 sessionctx/variable/sysvar.go    |  8 +-------
 sessionctx/variable/tidb_vars.go |  2 --
 3 files changed, 6 insertions(+), 31 deletions(-)

diff --git a/server/server.go b/server/server.go
index e4a009f7f1937..aa5a5f744d38b 100644
--- a/server/server.go
+++ b/server/server.go
@@ -302,7 +302,6 @@ func NewServer(cfg *config.Config, driver IDriver) (*Server, error) {
 	rand.Seed(time.Now().UTC().UnixNano())
 
 	variable.RegisterStatistics(s)
-	variable.SetMaxConnections = s.SetMaxConnections
 
 	return s, nil
 }
@@ -515,11 +514,14 @@ func (s *Server) onConn(conn *clientConn) {
 			})
 			terror.Log(err)
 		}
-		if errors.Cause(err) == io.EOF {
+		switch errors.Cause(err) {
+		case io.EOF:
 			// `EOF` means the connection is closed normally, we do not treat it as a noticeable error and log it in 'DEBUG' level.
 			logutil.BgLogger().With(zap.Uint64("conn", conn.connectionID)).
 				Debug("EOF", zap.String("remote addr", conn.bufReadConn.RemoteAddr().String()))
-		} else {
+		case errConCount:
+			_ = conn.writeError(ctx, err)
+		default:
 			metrics.HandShakeErrorCounter.Inc()
 			logutil.BgLogger().With(zap.Uint64("conn", conn.connectionID)).
 				Warn("Server.onConn handshake", zap.Error(err),
@@ -623,25 +625,6 @@ func (s *Server) checkConnectionCount() error {
 	return nil
 }
 
-// SetMaxConnections checks and updates the value of max_connections.
-func (s *Server) SetMaxConnections(newMaxConnections uint32) error {
-	// When the value of newMaxConnections is 0, the number of connections is unlimited.
-	if int(newMaxConnections) == 0 {
-		return nil
-	}
-
-	s.rwlock.RLock()
-	conns := len(s.clients)
-	s.rwlock.RUnlock()
-
-	if conns > int(newMaxConnections) {
-		logutil.BgLogger().Error("Current connections number exceeds the setting value",
-			zap.Uint32("max connections", newMaxConnections), zap.Error(errConCount))
-		return errConCount
-	}
-	return nil
-}
-
 // ShowProcessList implements the SessionManager interface.
 func (s *Server) ShowProcessList() map[uint64]*util.ProcessInfo {
 	rs := make(map[uint64]*util.ProcessInfo)
diff --git a/sessionctx/variable/sysvar.go b/sessionctx/variable/sysvar.go
index fd870e912c8d6..01879fde2943c 100644
--- a/sessionctx/variable/sysvar.go
+++ b/sessionctx/variable/sysvar.go
@@ -416,13 +416,7 @@ var defaultSysVars = []*SysVar{
 		return config.GetGlobalConfig().Instance.PluginDir, nil
 	}},
 	{Scope: ScopeInstance, Name: MaxConnections, Value: strconv.FormatUint(uint64(config.GetGlobalConfig().Instance.MaxConnections), 10), Type: TypeUnsigned, MinValue: 0, MaxValue: 100000, SetGlobal: func(s *SessionVars, val string) error {
-		newVal := uint32(TidbOptInt64(val, 0))
-		if SetMaxConnections != nil {
-			if err := SetMaxConnections(newVal); err != nil {
-				return err
-			}
-		}
-		config.GetGlobalConfig().Instance.MaxConnections = newVal
+		config.GetGlobalConfig().Instance.MaxConnections = uint32(TidbOptInt64(val, 0))
 		return nil
 	}, GetGlobal: func(s *SessionVars) (string, error) {
 		return strconv.FormatUint(uint64(config.GetGlobalConfig().Instance.MaxConnections), 10), nil
diff --git a/sessionctx/variable/tidb_vars.go b/sessionctx/variable/tidb_vars.go
index 657e88d161398..64c1916292c73 100644
--- a/sessionctx/variable/tidb_vars.go
+++ b/sessionctx/variable/tidb_vars.go
@@ -994,6 +994,4 @@ var (
 	GetMemQuotaAnalyze func() int64 = nil
 	// SetStatsCacheCapacity is the func registered by domain to set statsCache memory quota.
 	SetStatsCacheCapacity atomic.Value
-	// SetMaxConnections is the func registered by server to set the value of max_connections.
-	SetMaxConnections func(newMaxConnections uint32) error = nil
 )