Hi, I am one of the authors of this post.

The number 4 billion is made-up. It was chosen in order to illustrate the scale of the problem we are trying to solve. And it also happens to be just below the maximum number possible to store in an unsigned 4 byte integer. This is of course beneficial when trying to build an index with a small footprint. With more queries, we would have to consider using long integers (8 bytes) or some custom type with e.g. 5 bytes.

If you're interested in where the queries come from, you might find these previous posts interesting: https://0x65.dev/blog/2019-12-05/a-new-search-engine.html https://0x65.dev/blog/2019-12-06/building-a-search-engine-fr...