The Queue Reader Agent is used with snapshot replication or transactional replication with the queued updating option, or if the immediate updating with queued updating as a failover option is enabled.

The Queue Reader Agent is a multithreaded agent that runs on the Distributor. It is responsible for taking messages from a queue and applying them to the appropriate publication.

The Queue Reader Agent reads messages from the Microsoft® SQL Server™ 2000 queue on each Subscriber and applies the transactions to the publication. This agent uses the security context of SQL Server Agent by default. Unlike the Distribution Agent and the Merge Agent, only one instance of the Queue Reader Agent exists to service all Publishers and publications for a given Distributor.