Replication Architecture - Part 2 | SansSQL

Tuesday, December 25, 2012

Replication Architecture - Part 2

Let me get straight into the topic "Replication Architecture - Part 1"discussed last time; about the working of replication and then the entities involved in any replication model for that matter. We also did a understanding on publishing industry in comparison with replication which helped us in identifying the entities.

Following are the same:
  • Publisher
  • Distributor
  • Agent
  • Subscriber
  • Articles
  • Publications
  • Subscriptions
So, let us get into each of this with respect to Replication.
A SQL server instance can be configured as Publisher or Distributor or subscriber.

Publisher: In simple terms, Publisher is the server on which the "Source" database resides. It is the main source for data and also identifies what data should be distributed across.

Distributor: gathers all the published data and holds the same until it sends it across to all the registered subscribers. It is also referred to as "Bridge" between publisher-subscriber and can support multiple publisher and subscriber concept.

Subscriber: Is the final destination on which data has to be transmitted.

Articles: This is the basic unit of replication. An article identifies a database object that is included in a publication. A publication can contain different types of articles, including tables, views, stored procedures, and other objects.

Publication: A publication is a collection of one or more articles from one database. The grouping of multiple articles into a publication makes it easier to specify a logically related set of database objects and data that are replicated as a unit.

Subscription: A subscription is a request for a copy of a publication to be delivered to a Subscriber. The subscription defines what publication will be received, where, and when. There are two types of subscriptions, push and pull.

Agent: An agent is a median which identifies the changes at publisher and transfers those changes to subscriber.
There are different agents in replication,
  • Distribution Agent
  • Log Reader Agent
  • Merge Agent
  • Queue Reader Agent
  • Snapshot Agent