If some or all your tables need to be upgraded to MySQL’s latest storage engine (InnoDB) and row format (Dynamic) you see a notice about that.
Some of your tables may have many rows in them, and the Add Keys Now operation will take time. You may prefer to add keys to those tables one at a time, especially if you use a budget hosting service.
Alternatively, you may prefer to use WP-CLI, WordPress’s command-line interface for this operation, if you have access to it. WP-CLI doesn’t time out. If you’re not sure whether you have command line access, ask your hosting service.
As an example, you can add keys to your
wp_postmeta table with this command line.
wp index-mysql enable wp_postmeta
Or, to add keys to all tables you can use this command line
wp index-mysql enable --all
What keys do we add?
Please see here for details.