For each page view by a registered user we update the access value in the users table. For this mysql acquires a write lock which then blocks a lot of reads which want to read from the users table (which happens also each page view, and often more than once). On a high-traffic site such as drupal.org this can decrease mysql performance. For this reason and due to the fact that the access value is hardly ever used (all I found was the user table on /admin/user) I propose to move the access value into its own table, users_access. Attached patch does just that.
Closed: duplicate
9.5
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
#1835496: Factor {users_field_data}.access out of the table and entity caches → is a duplicate. It's newer but has a better issue summary (this one is outdated since comment ~#41), so closing this one.