Distributor, Publisher, then Subscriber. You always perform an upgrade in this order: distributor, publisher, subscriber.
The angle between the x-axis and a ray.
This is a mathematical function that returns the angle between the positive x-axis and the ray that passes through the two coordinates passed in. The angle is in radians.
The DCM tracks changes. The differential backup reads the extents from this structure. A differential backup uses the Differential Change Map to determine which extents have changed and need to be include in the backup. This greatly speeds the differential backup process.
This agent reads the subscriber logs and moves changes back to the publisher. This agent is used when the queued update model is chosen with transactional replication. It moves changes from the subscribers back to the publishers.