config, server: change the default value of max-server-connections

config/config.go

@@ -526,7 +526,7 @@ var defaultConf = Config{
 	SplitRegionMaxNum:            1000,
 	RepairMode:                   false,
 	RepairTableList:              []string{},
-	MaxServerConnections:         4096,
+	MaxServerConnections:         0,
 	TxnLocalLatches: TxnLocalLatches{
 		Enabled:  false,
 		Capacity: 2048000,

config/config.toml.example

@@ -99,8 +99,8 @@ repair-mode = false
 # In repair mode, repairing table which is not in repair list will get wrong database or wrong table error.
 repair-table-list = []
 
-# The maximum permitted number of simultaneous client connections.
-max-server-connections = 4096
+# The maximum permitted number of simultaneous client connections. When the value is 0, the number of connections is unlimited.
+max-server-connections = 0
 
 # Whether new collations are enabled, as indicated by its name, this configuration entry take effect ONLY when a TiDB cluster bootstraps for the first time.
 new_collations_enabled_on_first_bootstrap = false

config/config_test.go

@@ -171,6 +171,7 @@ unrecognized-option-test = true
 	c.Assert(f.Sync(), IsNil)
 
 	c.Assert(conf.Load(configFile), ErrorMatches, "(?:.|\n)*unknown configuration option(?:.|\n)*")
+	c.Assert(conf.MaxServerConnections, Equals, uint32(0))
 
 	f.Truncate(0)
 	f.Seek(0, 0)

server/server.go

@@ -458,6 +458,11 @@ func (cc *clientConn) connectInfo() *variable.ConnectionInfo {
 }
 
 func (s *Server) checkConnectionCount() error {
+	// When the value of MaxServerConnections is 0, the number of connections is unlimited.
+	if int(s.cfg.MaxServerConnections) == 0 {
+		return nil
+	}
+
 	s.rwlock.RLock()
 	conns := len(s.clients)
 	s.rwlock.RUnlock()