What you're hoping for is that some cacheable function of many documents is also a monoid. In an example, you're hoping that when you invalidate the query "SEL

What you're hoping for is that some cacheable function of many documents is also a monoid. In an example, you're hoping that when you invalidate the query "SELECT COUNT(*) FROM foo WHERE x = 1" because a new document that matched came in, you're simply incrementing the existing cached value, rather than rescanning the database index.