For internal purposes, a 64 bit GUID will be sufficient. Look how Twitter uses Snowflake - https://github.com/twitter/snowflake https://github.com/twitter/snowf

For internal purposes, a 64 bit GUID will be sufficient. Look how Twitter uses Snowflake - https://github.com/twitter/snowflake https://github.com/twitter/snowflake - that's a scalable way to generate unique IDs which won't ever be revealed to the user. For default user names, I quite like how gfycat does it - http://gfycat.com/about http://gfycat.com/about - AdjectiveAdjectiveAnimal - so a user is given a default name like "ReluctantCandidWombat". Fun, unique, hard to iterate, and hopefully provides an incentive to the user to change it later.