Why this change?
Backfilling can take a long time on a site with many users. As a
result, the `DistriburedMutex` will warn in the logs when the block takes
more than 60 seconds to complete. We can increase the lock validity but
the method is currently only called from a job which has a
`cluster_concurrency` set to `1`. Therefore, it is actually not
necessary for us to hold a `DistributedMutex` here.
What does this change do?
1. Removes the distributed mutex and adds a comment about the risk of
calling the `SidebarSiteSettingsBackfiller#backfill!` method.a
2. Delete old sidebar category section links in batches for all users
to avoid a single long running query.
Communities can use sidebar or header dropdown, therefore navigation menu is a better name settings in 2 places:
- Old user sidebar preferences;
- Site setting about default tags and categories.
The previous sidebar default tags and categories implementation did not
allow for a user to configure their sidebar to have no categories or
tags. This commit changes how the defaults are applied. When a user is being created,
we create the SidebarSectionLink records based on the `default_sidebar_categories` and
`default_sidebar_tags` site settings. SidebarSectionLink records are
only created for categories and tags which the user has visibility on at
the point of user creation.
With this change, we're also adding the ability for admins to apply
changes to the `default_sidebar_categories` and `default_sidebar_tags`
site settings historically when changing their site setting. When a new
category/tag has been added to the default, the new category/tag will be
added to the sidebar for all users if the admin elects to apply the changes historically.
Like wise when a tag/category is removed, the tag/category will be
removed from the sidebar for all users if the admin elects to apply the
changes historically.
Internal Ref: /t/73500
