*: tiny clean up (pingcap#3542)

server/conn.go

@@ -343,7 +343,8 @@ func (cc *clientConn) Run() {
 		data, err := cc.readPacket()
 		if err != nil {
 			if terror.ErrorNotEqual(err, io.EOF) {
-				log.Error(errors.ErrorStack(err))
+				log.Error("[%d] read packet error, close this connection %s",
+					cc.connectionID, errors.ErrorStack(err))
 			}
 			return
 		}

server/conn_stmt.go

@@ -118,12 +118,12 @@ func (cc *clientConn) handleStmtExecute(data []byte) (err error) {
 
 	flag := data[pos]
 	pos++
-	//now we only support CURSOR_TYPE_NO_CURSOR flag
+	// Now we only support CURSOR_TYPE_NO_CURSOR flag.
 	if flag != 0 {
 		return mysql.NewErrf(mysql.ErrUnknown, "unsupported flag %d", flag)
 	}
 
-	//skip iteration-count, always 1
+	// skip iteration-count, always 1
 	pos += 4
 
 	var (

server/server.go

@@ -155,8 +155,7 @@ func NewServer(cfg *Config, driver IDriver) (*Server, error) {
 
 // Run runs the server.
 func (s *Server) Run() error {
-
-	// Start http api to report tidb info such as tps.
+	// Start HTTP API to report tidb info such as TPS.
 	if s.cfg.ReportStatus {
 		s.startStatusHTTP()
 	}

session.go

@@ -58,10 +58,10 @@ import (
 type Session interface {
 	context.Context
 	Status() uint16                              // Flag of current status, such as autocommit.
-	LastInsertID() uint64                        // Last inserted auto_increment id.
+	LastInsertID() uint64                        // LastInsertID is the last inserted auto_increment ID.
 	AffectedRows() uint64                        // Affected rows by latest executed stmt.
 	Execute(sql string) ([]ast.RecordSet, error) // Execute a sql statement.
-	String() string                              // For debug
+	String() string                              // String is used to debug.
 	CommitTxn() error
 	RollbackTxn() error
 	// PrepareStmt executes prepare statement in binary protocol.
@@ -602,7 +602,7 @@ func (s *session) Execute(sql string) ([]ast.RecordSet, error) {
 	for i, rst := range rawStmts {
 		s.prepareTxnCtx()
 		startTS := time.Now()
-		// Some execution is done in compile stage, so we reset it before compile.
+		// Some executions are done in compile stage, so we reset them before compile.
 		executor.ResetStmtCtx(s, rst)
 		st, err1 := Compile(s, rst)
 		if err1 != nil {