What potential pitfalls should be considered when generating random keys for URLs in PHP?

One potential pitfall when generating random keys for URLs in PHP is the possibility of collisions, where two keys are the same. To mitigate this risk, it is important to use a secure random number generator and ensure that the generated keys are unique. One way to achieve this is by checking if the generated key already exists in a database or by using a function like `uniqid()` which includes the current timestamp to make the keys more unique.

$key = uniqid();
// Check if the key already exists in the database
// If it does, generate a new key