KEY
The key alone.
The one projection that can leave a document unread: where the plan proves the index already decided the answer, a keys-only query opens nothing. That is what makes documentsRead == 0 reachable rather than aspirational.
The key alone.
The one projection that can leave a document unread: where the plan proves the index already decided the answer, a keys-only query opens nothing. That is what makes documentsRead == 0 reachable rather than aspirational.