Creating indexes to improve efficiency

One of the rules of efficiency is to avoid search. Our previous example of using an iterator over the keys in a shelf is inefficient. To state that more strongly, search defines inefficiency. We'll emphasize this.

Tip

Brute-force search is perhaps the worst possible way to work with data. We must always design indexes that are based on subsets or mappings to improve performance.

To avoid searching, we need to create indexes that list the items we want. This saves reading through the entire shelf to find an item or subset of items. A shelf index can't reference Python objects, as that would change the granularity at which the objects are stored. A shelf index must only list key values. This makes navigation among objects indirect but still much faster than a brute-force search of all items in the shelf.

As an example of an index, we can keep a list of the Post keys associated with each Blog in the shelf. We can easily change the add_blog(), add_post(), and...