1. Integers: Integers are used in aggregations, comparisons,
and grouping. Timestamps are also stored as integers.
2. Strings: Strings are used for comparisons and grouping.
3. Sets of Strings: Sets of strings are used to represent, say,
words in a Facebook post or the set of features (such as graph
search, news feed redesign, etc.) that are true for a given user.
4. Vectors of Strings: Vectors of strings are ordered and are
mostly used for stack traces, where the order corresponds to
the stack level