Generate 5 million unique codes - php

Question

I am looking for an efficient way to generate 5 million unique codes with 7 characters (letters, numbers, special chars).
Basically, my idea was to generate a table with a unique constraint. Then to generate a code, insert it into the database, see if it is "accepted" (meaning a new code) until we have 5 million unique codes.
Alternatively they idea was to generate an array with 5 million unique codes to insert them afterward at once into the database to see how many of the codes make it into the database (are unique).
The third option was to create one code, check if it already exists, if not insert it into the database.
My question now is what method I should use - there might be a problem I oversee. Or is there a better way?
Thanks a lot!

Answer 1

Pick an appropriate function to generate one random code; for illustration purposes I'll be using this:
function generateCode() {
return substr(bin2hex(random_bytes(4)), 0, 7);
}
See https://stackoverflow.com/a/22829048/476 and other answers in there to pick something that works for you. The important point is that it uses a good source of randomness, either random_bytes, random_int, openssl_random_pseudo_bytes or /dev/urandom. This minimises the chance of two calls to this function producing the same output.
From there, simply use array keys to deduplicate the values:
$codes = [];
while (count($codes) < 5000000) {
$codes[generateCode()] = null;
}
$codes = array_keys($codes);
If generateCode is sufficiently random, there should be few collisions and there shouldn't be too much overhead in generating codes this way. Even if, this is presumably a one-time operation, and efficiency isn't paramount. 5 million short strings should certainly fit into memory without much problem. You can then insert them all into the database in a batch.

Answer 2

function generateRandomString($length = 7) {
// you can update these with new chars
$characters = '!##$%^&*()_+0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
$charactersLength = strlen($characters);
$randomString = '';
for ($i = 0; $i < $charactersLength; $i++) {
$randomString .= $characters[rand(0, $charactersLength - 1)];
}
return $randomString;
}
Now use an array to store the codes:
$codes = array();
while(count($codes)!=5000000){
$code = generateRandomString();
$codes[$code] = $code;
}
$codes key and value, both have the same code.

Answer 3

Given the purpose for which you're generating unique identifiers (as hard-to-guess coupon codes), I want to say that you should generate a unique identifier that combines a "unique" part and a "random" part.
The "unique" part can be a monotonically increasing counter (such as an auto-incremented row number in supporting databases), which can optionally serve as the seed of a full-period linear congruential generator (which cycles pseudorandomly through all possible values in its period before repeating).
The "random" part is simply a random number generated with a cryptographic random number generator (which for PHP is random_int). In general, the longer the random part is, the less predictable it will be.
Moreover, for the purposes of generating unique coupon codes, there is little reason to limit yourself to 7-character codes, especially if end users won't be required to enter those codes directly. See also this question.

Answer 4

Should the codes you wanted needed to be inserted in the database?
It would have been better not to constantly request to the db and try if it is unique.
You can store the codes to an array, first before putting it to the db.
Pseudo-code:
Generate unique 5 million codes, inserted in the hash table or an array. // as you insert a new one check the hash-table if it exists.
You then insert this hash table or array in the database now.