Fix #589 (#592)

Author: daviszhen

pkg/frontend/mysql_cmd_executor.go

@@ -868,6 +868,33 @@ func (mce *MysqlCmdExecutor) handleSelectDatabase(sel *tree.Select) error {
 	return nil
 }
 
+/*
+handle "SELECT @@max_allowed_packet"
+ */
+func (mce *MysqlCmdExecutor) handleMaxAllowedPacket() error {
+	var err error = nil
+	ses := mce.routine.GetSession()
+	proto := mce.routine.GetClientProtocol().(*MysqlProtocol)
+
+	col := new(MysqlColumn)
+	col.SetColumnType(defines.MYSQL_TYPE_LONG)
+	col.SetName("@@max_allowed_packet")
+	ses.Mrs.AddColumn(col)
+
+	var data = make([]interface{},1)
+	//16MB
+	data[0] = 16777216
+	ses.Mrs.AddRow(data)
+
+	mer := NewMysqlExecutionResult(0, 0, 0, 0, ses.Mrs)
+	resp := NewResponse(ResultResponse, 0, int(COM_QUERY), mer)
+
+	if err := proto.SendResponse(resp); err != nil {
+		return fmt.Errorf("routine send response failed. error:%v ", err)
+	}
+	return err
+}
+
 /*
 handle Load Data statement
  */
@@ -1012,6 +1039,16 @@ func (mce *MysqlCmdExecutor) doComQuery(sql string) error {
 								continue
 							}
 						}
+					}else if ve, ok := sc.Exprs[0].Expr.(*tree.VarExpr); ok {
+						if strings.ToLower(ve.Name) == "max_allowed_packet" {
+							err = mce.handleMaxAllowedPacket()
+							if err != nil {
+								return err
+							}
+
+							//next statement
+							continue
+						}
 					}
 				}
 			}