What is the difference between pull-push and pub-sub?

Pull-Push describes a mechanism of interaction where the consumer (initiator) actively requests data (pull) from the source, or the source actively sends data (push) to the consumer. In system contexts, this can be a client regularly polling a server (pull), or a server sending notifications to clients (push).

Pub-Sub (Publish-Subscribe) is a message exchange design pattern where there are publishers (publishers) and subscribers (subscribers). Publishers publish messages to a specific topic or channel without knowing who will receive them. Subscribers register for topics of interest and receive all messages published to those topics. The intermediary between publishers and subscribers is typically a message broker.

Main difference:

Pull-Push focuses on the initiator of data transfer (source or consumer), while Pub-Sub focuses on the interaction pattern between participants through an intermediary and topics. Pub-Sub is often implemented on top of pull or push mechanisms. For example, a subscriber may use pull to receive messages from the broker, or the broker may use push to send messages to subscribers.