How to implement “autoincrement” on Google AppEngine

Question

I have to label something in a \"strong monotone increasing\" fashion. Be it Invoice Numbers, shipping label numbers or the like.

1. A number MUST NOT BE used twi

Answer 1

If you absolutely have to have sequentially increasing numbers with no gaps, you'll need to use a single entity, which you update in a transaction to 'consume' each new number. You'll be limited, in practice, to about 1-5 numbers generated per second - which sounds like it'll be fine for your requirements.