Major Description
Certain operations in the query engine like getting the size of a result set or facets are expensive to compute due to the fact that ACLs need to be computed on the entire result set. This issue is to discuss an idea how we could improve this:
There is a very common special case: content (a subtree) that is readable by everyone (anonymous). If we mark an index on that subtree as "readable by everyone" on index creation then we could skip ACL check on the result set or precompute/cache certain query results.
In order to avoid information leakage the index would have to be marked "invalid" as soon as one node in that sub-tree is not readable by everyone anymore. (could be checked through a commit hook)
Maybe this concept could even be generalized later to work with other principals than everyone.
Just an idea - feel free to poke holes and shoot it down 