Changes in MySQL 8.0 •Step 2 marks all checked and repaired tables with the current MySQL version number. This ensures that the next time upgrade checking occurs with the same version of the server, it can be determined whether there is any need to check or repair a given table again. •Step 2 upgrades the system tables to ensure that they have the current structure. This is true whether the server or  mysql_upgrade  performs the step. With respect to the content of the help tables and time zone tables,  mysql_upgrade  does not load either type of table, whereas the server loads the help tables, but not the time zone tables. (That is, prior to MySQL 8.0.16, the server loads the help tables only at data directory initialization time. As of MySQL 8.0.16, it loads the help tables at initialization and upgrade time.) The procedure for loading time zone tables is platform dependent and requires decision making by the DBA, so it cannot be done automatically. 2.11.4 Changes in MySQL 8.0 Before upgrading to MySQL 8.0, review the changes described in this section to identify those that apply to your current MySQL installation and applications. Perform any recommended actions. Changes marked as  Incompatible change  are incompatibilities with earlier versions of MySQL, and may require your attention  before upgrading . Our aim is to avoid these changes, but occasionally they are necessary to correct problems that would be worse than an incompatibility between releases. If an upgrade issue applicable to your installation involves an incompatibility, follow the instructions given in the description. MySQL Server 8.0 incorporates a global data dictionary containing information about database objects in transactional tables. In previous MySQL series, dictionary data was stored in metadata files and nontransactional system tables. As a result, the upgrade procedure requires that you verify the upgrade readiness of your installation by checking specific prerequisites. For more information, see Section 2.11.5, “Preparing Your Installation for Upgrade” . A data dictionary-enabled server entails some general operational differences; see Section 14.7, “Data Dictionary Usage Differences” . •Data Dictionary Changes •caching_sha2_password as the Preferred Authentication Plugin •Configuration Changes •Server Changes •InnoDB Changes •SQL Changes •Changed Server Defaults Data Dictionary Changes caching_sha2_password as the Preferred Authentication Plugin The  caching_sha2_password  and  sha256_password  authentication plugins provide more secure password encryption than the  mysql_native_password  plugin, and  caching_sha2_password provides better performance than  sha256_password . Due to these superior security and performance characteristics of  caching_sha2_password , it is as of MySQL 8.0 the preferred authentication plugin, and is also the default authentication plugin rather than  mysql_native_password . This change affects both the server and the  libmysqlclient  client library: •For the server, the default value of the  default_authentication_plugin  system variable changes from  mysql_native_password  to  caching_sha2_password . 267