So one way to optimize this is to use incremental IDs. However, when using incremental IDs, insertion can be much easier вЂ“ just go to the last page. Since IDs are not sequential, so every time a new record is inserted, the database needs to go look at the correct page for this ID. More specifically, when you already have millions of records, insertion can be costly. If you dig into the insert/query process, you will notice that using random string as IDs may sacrifice performance a little bit.

One thing IвЂ™d like to further discuss here is that by using GUID (Globally Unique Identifier) as the entry ID, what would be pros/cons versus incremental ID in this problem? There are quite a few follow-up questions for this problem. In the run time, when someone visits, we look up by ID вЂњabcd123вЂќ and redirect to the corresponding URL вЂњ вЂќ. When a user inputs a long URL вЂњвЂќ, the system creates a random 7-character string like вЂњabcd123вЂќ as ID and inserts entry into the database. A straightforward approach is using alias_hash as the ID of each mapping, which can be generated as a random string of length 7. To begin with, letвЂ™s store all the mappings in a single database. ItвЂ™s said that there are ~644 million URLs at the time of this writing. If the length is 7 containing, we can serve 62 ^ 7 ~= 3500 billion URLs. To make things easier, we can assume the alias is something like and alias_hash is a fixed length string. The second condition is the core as in the run time, the system should look up by alias and redirect to the corresponding URL quickly. Each alias can be mapped back to a unique URL easily.Each URL can only be mapped to a unique alias.Therefore, the question can be simplified like this вЂ“ given a URL, how can we find hash function F that maps URL to a short alias: I would expect you to think about something related to hash immediately.

LetвЂ™s get started with basic and high-level solutions and we can keep optimizing it later on.ДЄt first glance, each long URL and the corresponding alias form a key-value pair. So if you would design this system that allows people input URLs with short alias URLs generated, how would you do it? If you click the alias, itвЂ™ll redirect you to the original URL. There are many other similar services like Google URL Shortener, Bitly etc.ДЇor example, URL is long and hard to remember, TinyURL can create a alias for it вЂ“. Basically, TinyURL is a URL shortening service, a web service that provides short aliases for redirection of long URLs.

If you are not familiar with TinyRUL, IвЂ™ll briefly explain here. If you are new to system design interview, IвЂ™d highly recommend you take a look at 8 Things You Need to Know Before a System Design Interview first, which provides general strategies that can help you get started. IвЂ™d like to summarize how weвЂ™ll analyze this problem with high-level thoughts here. This week, Gainlo team has brainstormed tons of ideas about this interview question. Assume we have an alphabet of 58 characters (reason in the implementation section) for the short id, here is a table about the number of distinct short id of the given length.If you have started preparing for system design interviews, you must have heard of one of the most popular question вЂ“ create a TinyURL system. We also need to determine the length of the short id, which should be as short as possible. Suppose the read to write ratio is 10:1, we need to handle 600 redirection requests at peak. Suppose the peak traffic is 5 times of the average, our system should be able to handle 60 shortening requests per second at peak. We have 1000000/86400в‰€12 requests per second on average. Then there are 3 million new links per day and about 1 billion per year. Suppose we have 1 million DAU(Daily Active User) and each user make 3 shortening requests per day. Let's do some estimation and calculation. In practice, we often need to support additional fields like custom_alias and expiry_date. Response: short is the short id encoded in Base58. Request: longURL is the long URL to be shortened. APIДЇor simplicity, our demo will not have user authentication and all requests are made anonymously.ДЈ02 redirects to the long URL if the short id is valid, otherwise return 404 not found. We will design a scalable URL shortening service with real demo code. You can read more about how URL redirection works on MDN. And when you post a link on Twitter, it will automatically generate a short URL, such as t.co/tfIrCKKUrd. It can generate a short URL /algomo that redirects to algo.monster. One of the most popular services is TinyURL. URL Shorteners are widely used on the Internet.

Tinyurl system design