Do not stick to primary after recording last_activity_on

This reduces requests using the primary DB by the number of users using
the site every day (since last_activity_on is update at most once per
day per user).

app/services/users/activity_service.rb

@@ -37,3 +37,5 @@ module Users
     end
   end
 end
+
+Users::ActivityService.prepend_ee_mod

ee/app/services/ee/users/activity_service.rb

+# frozen_string_literal: true
+
+module EE
+  module Users
+    module ActivityService
+      extend ::Gitlab::Utils::Override
+
+      private
+
+      override :record_activity
+      def record_activity
+        ::Gitlab::Database::LoadBalancing::Session.without_sticky_writes { super }
+      end
+    end
+  end
+end

ee/changelogs/unreleased/not_stick_after_activity.yml

+---
+title: Do not stick to primary after recording User#last_activity_on
+merge_request: 57212
+author:
+type: performance

ee/spec/services/users/activity_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Users::ActivityService, '#execute', :request_store, :redis, :clean_gitlab_redis_shared_state do
+  let(:user) { create(:user, last_activity_on: last_activity_on) }
+
+  context 'when last activity is in the past' do
+    let(:user) { create(:user, last_activity_on: Date.today - 1.week) }
+
+    context 'database load balancing is configured' do
+      before do
+        # Do not pollute AR for other tests, but rather simulate effect of configure_proxy.
+        allow(ActiveRecord::Base.singleton_class).to receive(:prepend)
+        ::Gitlab::Database::LoadBalancing.configure_proxy
+        allow(ActiveRecord::Base).to receive(:connection).and_return(::Gitlab::Database::LoadBalancing.proxy)
+      end
+
+      let(:service) do
+        service = described_class.new(user)
+
+        ::Gitlab::Database::LoadBalancing::Session.clear_session
+
+        service
+      end
+
+      it 'does not stick to primary' do
+        expect(::Gitlab::Database::LoadBalancing::Session.current).not_to be_performed_write
+
+        service.execute
+
+        expect(user.last_activity_on).to eq(Date.today)
+        expect(::Gitlab::Database::LoadBalancing::Session.current).to be_performed_write
+        expect(::Gitlab::Database::LoadBalancing::Session.current).not_to be_using_primary
+      end
+
+      after do
+        ::Gitlab::Database::LoadBalancing.clear_configuration
+      end
+    end
+
+    context 'database load balancing is not configured' do
+      let(:service) { described_class.new(user) }
+
+      it 'updates user without error' do
+        service.execute
+
+        expect(user.last_activity_on).to eq(Date.today)
+      end
+    end
+  end
+end