I see how CLUSTER can speed up a range query (eg WHERE val < 30),
because it groups those records in contiguous pages.
What about where I'm only pulling one record back? Eg WHERE user_id =
100. Is there any benefit to a CLUSTER in that case? Is there
anything lost if I CLUSTER on a different index?
If my usage is: A large number of single record SELECTs based on
user_id, and a small number of range queries, usually based on val,
would I be best off CLUSTERing on val?