Implementing a distributed database system in SQL Server involves spreading your database across multiple machines to improve performance, availability, and scalability. SQL Server offers several technologies to support distributed databases, including linked servers, replication, and Always On Availability Groups.

Understanding Distributed Databases

A distributed database system consists of a single logical database that is spread across more than one node or location, each node potentially being a different database system. The primary advantages of such a system include:

• Load Balancing: Distributes database queries across multiple servers to improve performance.
• High Availability: Increases availability through redundancy; if one server fails, another can take over.
• Scalability: Allows adding more servers to handle increased load.

SQL Server and Distributed Database Technologies

SQL Server supports various methods to manage distributed databases:

1. Linked Servers: SQL Server allows the configuration of linked servers which can be used to execute commands across different database servers. This facilitates queries that span multiple databases, either SQL Server instances or other database types that supports OLE DB.
2. Replication: Replication involves distributing and synchronizing data across multiple servers. SQL Server has various replication strategies like merge, transactional, and snapshot replication. Each type suits different use cases.
3. Always On Availability Groups: This is a high availability and disaster recovery solution introduced in SQL Server 2012. It allows databases to be copied across multiple instances of SQL Server in different locations.
4. SQL Server Integration Services (SSIS): Useful for integrating and moving data between diverse databases and data stores, often employed in large scale data migration and integration projects.

Implementation Steps

The implementation of a distributed database typically follows these stages:

Step 1: Designing the System

First, analyze needs and outcomes desired from the distributed system. Decide on the architecture—homogeneous (same DBMS) or heterogeneous (different DBMS types). Establish relationships between databases, and plan out replication or linking strategies.

Step 2: Configuring Linked Servers

To create a linked server in SQL Server Management Studio (SSMS):

• Right-click on the "Server Objects" folder, then choose "Linked Servers".
• Provide the necessary details such as product name, data source, and security settings.

Step 3: Setting Up Replication

Set up publishers, distributors, and subscribers, defining articles (data and database objects), and distribution agents manage synchronization.

Step 4: Configuring Always On Availability Groups

• Enable Windows Server Failover Clustering (WSFC).
• Use SQL Server Configuration Manager to enable Always On availability groups feature.
• Create availability groups and add databases to each group, configuring synchronization and failover settings.

Step 5: Testing and Optimization

Finally, extensively test every component to ensure data consistency and high availability. Performance tuning, indexing, and query optimization are crucial at this stage.

Use-Cases and Examples

Consider a e-commerce backend distributed across multiple geographic locations to reduce latency and handle local traffic efficiently:

• Linked Server: Connecting an inventory database in North America to an order processing database in Europe for real-time inventory updates.
• Replication: Using transactional replication to synchronize a central product database with multiple read-only subscriber databases in retail locations worldwide.
• Always On Availability Groups: Ensuring the availability of a critical payment processing database across data centers in Asia and North America.

Summary Table

Conclusion

Distributed databases in SQL Server involve multiple technologies each suited to different scenarios depending on the needs related to performance, availability, or data distribution. Proper design, careful implementation, and ongoing management are crucial for leveraging the full advantages of distributed databases within SQL Server environments.