Capacity estimation

Let's assume we'll store each shortened URL for 10 years.
Let's assume we'll create 1000 short URLs per second.
That's 1000 * 60 * 60 * 24 * 365 * 10 = 315360000000 = 315 billion URLs in 10 years
We'll use the A-Z,a-z,0-9 character set. Therefore we have 62 characters at our disposal.
62 ^ 1 = 62 unique URLs if we use 1-character URLs (< 315 billion)
62 ^ 6 = 56800235584 (56 billion) unique URLs if we use 6-character URLs (< 315 billion)
62 ^ 7 = 3,521,614,606,208 = 3.5 trillion unique URLs if we use 7-character URLs

We need to use at least 7 characters in our URLs.

Each short URL is approximately 7 bytes

Let's assume each long URL will be a maximum of 100 characters in length, therefore it's 100 bytes of storage

The user metadata and URL clicks info is about 500 bytes in size

Therefore, we have a ceiling of 1000 bytes to store for each URL (long, short, and user and URL clicks metadata)

For 315,360,000,000 URLs * 1000 bytes = 315,360,000,000,000 bytes = 315 Terabytes