DURABLE EXACTLY ONCE MESSAGE DELIVERY AT SCALE

The present invention extends to methods, systems, and computer program products for durable exactly once message delivery at scale. A message capture system uses a synchronous capture channel and transactions to provide durable exactly once message capture. Messages are sent from the message capture system to a message delivery system over a network using an at least once transfer protocol. The message delivery system implements a durable at most once messaging behavior, the combination of which results in durable exactly once transfer of messages from the message capture system to the message delivery system. The message delivery system uses a synchronous delivery channel and transactions to provide durable exactly once message delivery. Cursors maintaining message consumer state are collocated with message consumers, freeing up message log resources to process increased volumes of messages, such as, for example, in a queued or pub/sub environment.