The similarity of `Relation#uniq` to `Array#uniq` is confusing. Since our Relation API is close to SQL terms I renamed `#uniq` to `#distinct`. There is no deprecation. `#uniq` and `#uniq!` are aliases and will continue to work. I also updated the documentation to promote the use of `#distinct`.
We discussed that the auto explain feature is rarely used. This PR removes only the automatic explain. You can still display the explain output for any given relation using `ActiveRecord::Relation#explain`. As a side-effect this should also fix the connection problem during asset compilation (#9385). The auto explain initializer in the `ActiveRecord::Railtie` forced a connection.
Previously it returned an Array. If you want an array, call e.g. `Post.to_a` rather than `Post.all`. This is more explicit. In most cases this should not break existing code, since Relations use method_missing to delegate unknown methods to #to_a anyway.