Tech-Notes

URL Shortner

Data capacity Model

Column	memory	capacity
Long Url	2 kb	2048 chars
Short Url	17b	17 chars
Created at	7 bytes	7 chars
Expired at	7 bytes	7 chars
Total	2.031 kb

Note: for 30 Million users we generate
60.7 GB/month
0.7 TB/year
3.6 TB/5year

size of short url

www.us.com/abc1234

Random id generator:

1. MD5 hash - receive string and lengthy output. but lot of collision if we choose first 7 chars of it.
2. Base10 - generate only number output. 10^7=10million
3. Base64 - 2^36=68000 million(0.07trillion)
4. Base62 - receive number input and generate alphanumeric base62. 62^7=3.5trillion

Note: if we have 1000 hits/sec. it need 110 years to reach 3.5trillion
Possible alphanumberics are: a-z = 26
A-Z = 26
0-9 = 10
Total = 62

Code

public class Base62 {
    private static final char[] ALPHABET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz".toCharArray();

    public static String encode(long num) {
        StringBuilder sb = new StringBuilder();
        while (num > 0) {
            sb.append(ALPHABET[(int) (num % 62)]);
            num /= 62;
        }
        return sb.reverse().toString();
    }

    public static void main(String[] args) {
        long input = 1234567890L;
        String base62Code = encode(input);
        System.out.println("Base62 code: " + base62Code);
    }
}