I manage the server for a site with 30k+ posts. I've tried to update the site from WP 4.9.9 to current WP 5.0.2.
The update seems to work correctly, but then the backend becomes very slow, while the frontend keeps working normally.
After the update
mytop shows many
ALTER TABLE wp_posts ... post_password ... queries running, and, at the top, a copy operation for ALTER TABLE that takes most of the database time.
I tried letting it run for a whole day, but it didn't finish and I can't afford longer downtimes in the backend, so I've recovered the whole installation from backup, and now I'm back with WP 4.9.9.
I know many
ALTER TABLE statements in MySQL are implemented as create new table, copy over, delete old table, rename new table, and I assume this is just what I'm seeing.
However I couldn't find any documentation about that WP 5 update behavior, and I'd be surprised to find out it is actually WP doing that, and no one noticed it yet besides me. More likely I haven't googled properly, or it's not WP to blame, but some plugin.
Does WP really alter
wp_posts table upon upgrade to WP 5? And, if so, what can I do to workaround the problem?