http://blog.gainlo.co/index.php/2016/03/08/system-design-interview-question-create-tinyurl-system/

GUID(Globally Unique Identifier) as the entry ID, what would be pros/cons versus incremental ID in this problem?

If you dig into the insert/query process, you will notice that using random string as IDs may sacrifice performance a little bit. More specifically, when you already have millions of records, insertion can be costly. 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. However, when using incremental IDs, insertion can be much easier – just go to the last page.

Using incremental IDs. Every time a new URL is inserted, we increment the ID by 1 for the new entry. We also need a hash function that maps each integer ID to a 7-character string. If we think each string as a 62-base numeric, the mapping should be easy (Of course, there are other ways).

On the flip side, using incremental IDs will make the mapping less flexible. For instance, if the system allows users to set custom short URL, apparently GUID solution is easier because for whatever custom short URL, we can just calculate the corresponding hash as the entry ID.

Note: In this case, we may not use random generated key but a better hash function that maps any short URL into an ID, e.g. some traditional hash functions likeCRC32,SHA-1etc..