That's because the database fail with no changes made, and they retry the whole HTTP request with all business logic in the application re-run against primary i

That's because the database fail with no changes made, and they retry the whole HTTP request with all business logic in the application re-run against primary instance. So, nothing to do with database-level stuff. The idea is basically "there is an useful concept of 'group of queries' which is invisible to DB" :)