Introduction to Replication Tom Davis Software Architects, Inc.

Overview Introduction to Distributed Data Introduction to Replication Replication Agents Replication Types Physical Replication Models

Introduction to Distributed Data The Need for Distributed Data Considerations for Distributing Data Methods to Distribute Data

The Need for Distributed Data Brings Data Closer Together Allows Site Independence Separates OLTP Read Intensive Applications Can Reduce Conflicts

Distributed Data Considerations

Methods to Distribute Data

Introduction to Replication The Publisher-Subscriber Metaphor Publications and Articles Filtering Data Subscriptions

The Publisher-Subscriber Metaphor

Publications and Articles The basis of a subscription A collection of one or more articles Can have one or more publications per database Article Data from a whole or filtered partition of a table or a database object Part of a publication

Filtering Data

Subscriptions

Replication Agents Snapshot Agent Distribution Agent Log Reader Agent Prepares initial snapshots and stores them on the distributor Distribution Agent Moves snapshot and transactional data to Subscribers Log Reader Agent Copies data from transaction log to the distribution database Merge Agent Merges changes from multiple sites Queue Reader Agent Applies changes from a queue and applies them to multiple subscribers Cleanup Agents Complete scheduled and on-demand maintenance of replication

Replication Types Overview of the Replication Types Considerations for Using Merge Replication

Overview of the Replication Types Snapshot Replication Periodic bulk transfer of new snapshots of data Transactional Replication Replication of incremental changes Merge Replication Autonomous changes to replicated data are later merged

Considerations for Using Merge Replication Changes to the Schema Identifies a unique column Adds several system tables Creates triggers at Publisher and Subscriber Conflict resolution Tracks updates Compares values and resolves conflicts Replicates only synchronized data

Physical Replication Models Overview of the Physical Replication Models Combining Physical Replication Models and Types Central Publisher/Remote Distributor Example Central Subscriber/Multiple Publishers Example Multiple Publishers/Multiple Subscribers Example

Overview of the Physical Replication Models

Combining Physical Replication Models and Types The Model is the Physical Implementation The Type Provides the Functionality Any of the Models Can Use Any of the Types

Central Publisher/Remote Distributor Example

Central Subscriber/Multiple Publishers Example

Multiple Publishers/Multiple Subscribers Example

Recommended Practices Determine the Acceptable Degree of Data Latency Select an Appropriate Replication Type Select the Physical Replication Model Determine Whether to Allow Updates to Replicated Data