Cool! So if I select two columns with a predicate in the first, does it scan all stripes for the second column?
If I understand what you are asking, let me restate: "can you apply a predicate first on column A before reading column B, so that you can avoid reading column B if the predicate on A doesn't match?".
The answer is: "sometimes". Predicates match some rows and not others, so matching rows may be mixed in with non-matching rows, so it's not always possible to avoid the IO to read column B. However, if the matching and non-matching rows happen to be separated (e.g. if your table is naturally in time order and you have a time-based predicate), then it's able to do this optimization. Please see the section on "Chunk Group Filtering".