Auto-increment database IDs
Database auto-increment is something I find incredibly frustrating; pretty much every PHP/MySQL beginner tutorial teaches people to do this, but you really shouldn't.
I have got experience trying to shard auto-increment database IDs, and it's messy. Let's suppose you shard the database so the dataset over two database servers...how on earth can you expect someone to scale auto-increment IDs?
MySQL now even features a UUID function, allowing you to generate good IDs with strong entropy, meaning it also features a higher theoretical limit than auto-increment triggers on tables with an
int data type.
In order to use the UUID function, the database table should ideally be a CHAR(20).