Question

Since uniqid() provides a random string based on the value given, is it even possible, and if so, what are the chances of uniqid('foo') equalling uniqid('foo2')?

Answer 1

uniqid() does not provide a random value based on the string.

Per documentation:

Gets a prefixed unique identifier based on the current time in microseconds.

foo and foo2 will only be used to prefix the value. For example, this code:

echo uniqid('foo') . "\n";
echo uniqid('foo2');

would output:

foo510aac3bedcdb
foo2510aac3bedd03

As long as the prefix is different, the values won’t collide. However with the same prefix, a collision would be possible if the 2 requests are made at the same microsecond. If you are worried about collision, set the second parameter to true to add more entropy to your value.