diff --git a/app/controllers/sessions_controller.rb b/app/controllers/sessions_controller.rb
index 13e0a93c5..191bc1fa0 100644
--- a/app/controllers/sessions_controller.rb
+++ b/app/controllers/sessions_controller.rb
@@ -16,12 +16,6 @@ def new
 
   sig { void }
   def create
-    begin
-      clear_expired_sessions
-    rescue StandardError
-      # Cleanup is best effort; it must not block logging in.
-    end
-
     user, status = User.authenticate_with_status(params[:session][:login], params[:session][:password])
 
     case status
@@ -68,9 +62,4 @@ def try_to_redirect_incorrect_login(redirect_params = {})
         redirect_to login_path, redirect_params
       end
     end
-
-    sig { void }
-    def clear_expired_sessions
-      Session.delete_expired
-    end
 end
diff --git a/app/models/session.rb b/app/models/session.rb
index f7f359385..31a1907d0 100644
--- a/app/models/session.rb
+++ b/app/models/session.rb
@@ -3,10 +3,6 @@
 
 class Session < ActiveRecord::SessionStore::Session
   extend T::Sig
-  sig { returns(Integer) }
-  def self.delete_expired
-    where(updated_at: ...1.month.ago).delete_all
-  end
 
   sig { params(user: User).returns(T::Boolean) }
   def belongs_to?(user)
diff --git a/app/models/user.rb b/app/models/user.rb
index e72c5da07..e8430f1d5 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -39,8 +39,9 @@ class User < ApplicationRecord
   has_many :organization_memberships, dependent: :destroy
   has_many :memberships, through: :organization_memberships, source: :organization
 
+  # Case-sensitive so it uses index_users_on_login; a case-insensitive check scans every user on each signup.
   validates :login, presence: true,
-                    uniqueness: { case_sensitive: false },
+                    uniqueness: true,
                     length: { within: 2..50 }
 
   validates :email, presence: true,
diff --git a/spec/controllers/sessions_controller_spec.rb b/spec/controllers/sessions_controller_spec.rb
index 6f5196b98..4577d340d 100644
--- a/spec/controllers/sessions_controller_spec.rb
+++ b/spec/controllers/sessions_controller_spec.rb
@@ -77,6 +77,17 @@ def post_create
       end
     end
 
+    describe 'with stale sessions in the store' do
+      it 'does not delete them while logging in' do
+        stale = Session.create!(session_id: 'stale', data: {})
+        stale.update_column(:updated_at, 2.months.ago)
+
+        post_create
+
+        expect(Session.exists?(stale.id)).to be(true)
+      end
+    end
+
     describe 'when authentication fails' do
       before :each do
         allow(User).to receive(:authenticate_with_status).and_return([nil, :rejected])
diff --git a/spec/models/user_spec.rb b/spec/models/user_spec.rb
index 4f7c9b3a6..3f4f70e9e 100644
--- a/spec/models/user_spec.rb
+++ b/spec/models/user_spec.rb
@@ -112,6 +112,16 @@
       expect(user.errors[:login].size).to eq(1)
     end
 
+    it 'checks login uniqueness without scanning LOWER(login)' do
+      user = User.new(@params)
+      queries = []
+      callback = ->(*, payload) { queries << payload[:sql] }
+      ActiveSupport::Notifications.subscribed(callback, 'sql.active_record') { user.valid? }
+
+      expect(queries.grep(/"users"\."login"/)).not_to be_empty
+      expect(queries.grep(/LOWER\("users"\."login"\)/i)).to be_empty
+    end
+
     it 'should fail without email' do
       @params.delete(:email)