Replication Agents and Maintnance Jobs

There are bunch of agents and maintnance jobs to perform replication in SQL Server 2005. The following is their running location and sumary:

  • SnapShot Agent: Runs on distributor; used by All type replications.There is one agent for each publication; It prepares schema and initial data files of published tables and other objects, stores the snapshot files; It connects to Publisher and Distributor;
  • Logreader Agent: Runs on distributor; It’s used by transactional replication. Each database published using transactional replication has its own Log Reader Agent;  It moves transactions marked for replication from the transaction log on the Publisher to the distribution databaseIt; It connects to Publisher and Distributor;
  • Distribution Agent: Runs on Distributor for push subscriptions, and runs at the Subscriber for pull subscriptions. It’s used by snapshot replication and transactional replication; It applies the initial snapshot to the Subscriber and moves transactions held in the distribution database to Subscribers;  It connects to Subscriber and Distributor.
  • Merge Agent: It’s used with Merge Replication. It runs at the Distributor for push subscriptions and runs at the Subscriber for pull subscriptions; Used by Merge replication. It connects to Subscriber and Distributor; It applies the initial snapshot to the Subscriber, uploads changes from the Subscriber to the Publisher and then downloads changes from the Publisher to the Subscriber;
  • Queue Reader Agent: Runs at the Distributor; One instance of the Queue Reader Agent to service all Publishers and publications for a given distribution database. Used by transactional replication with the queued updating option;It connects to the Publisher,each Subscriber and the Distributor;
Replication Maintnance Jobs:
The following job runs at Publisher:
Expired subscription clean up;

The following jobs run at Distributor:
Distribution clean up;
Reinitialize subscriptions having data validation failures;
Agent history clean up;
Replication monitoring refresher for distribution;
Replication agents checkup;
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