Replication is a technique that is utilised to guarantee the availability of data, as well as its reliability and fault tolerance. 

This is accomplished by generating copies of the data across several servers or nodes with in a distributed system. '

Although SQL Server and Cassandra both make use of replication, the ways in which they implement and manage it are distinct from one another.

 

SQL Server Replication Types:

• Snapshot Replication: A snapshot of the data is collected from the publisher and applied to subscribers. Snapshots are good for small to medium databases or infrequent data updates.
• Transactional Replication: Based on transactional replication. It captures and replicates publisher-to-subscriber transactions in near real time. For high-throughput scenarios including boosting scalability and availability, data warehousing and reporting, integrating heterogeneous data from many sites, and outsourcing batch processing. Transaction replication works well in high-volume, fast-changing situations.
• Merge Replication: Involves sending data from Publisher to Subscribers, letting them update while connected or disconnected, then merging the updates when connected. Data is synchronised between servers continuously, on demand, or planned. Merging changes from different locations resolves disputes. Merge replication is good for synchronising updates from several locations.
• Peer-to-peer replication: involves the publisher server replicating data to numerous subscriber servers simultaneously. It maintains data copies across server instances, or nodes, to improve data availability and scalability. A centralised data centre oversees other data centres' data. Peer-to-peer replication works for global data centre coordination.

 

key participants in the Sql server Replication . 

• Publisher: The database that transmits data modifications. 
• Distributor: the replication process, storing metadata and historical data. 
• Subscriber: The database that is the intended recipient of data modifications from the publisher.

 

Best Practices for SQL Server Replication 

• Plan Replication Topology: Choose snapshot, transactional, or merge replication based on your use case. 
• Regularly assess replication performance and address lag. 
• Manage Conflicts: In merge replication, have conflict resolution mechanisms. 
• Data protection during replication: Use secure channels and authentication.

 

Type of Replication

• There are two possible replication methods: 
  Synchronous: The process of data replication can be carried out in real time (synchronous) 
• Asynchronous: The process of data replication can be carried out,  with a delay (asynchronous), depending on the individual's preference.

 

Use Cases

•  In distributed databases, backup systems, and data warehouses.
• A company might replicate its warehouse database across multiple data centers to ensure that if one data center goes down, the others can still serve the data.

 

Setting up a SQL Server replication
Involves setting up a replication involves configuring publications, defining articles, creating subscriptions, and monitoring the replication process. It's important to choose the appropriate type of replication depending on factors such as the size of the database, the frequency of data changes, and the specific use case requirements.

• Environment preparation
  Make sure replication permissions are established.
  Install required components on all participating servers.
• Make a distribution
  Name and describe the distribution.
  Configure replication distribution database.
  Select Publishers for Distributor access.
  The success window should appear when you finish.
• Create a publication
• Configure subscribers
• Initialize  subscribers
  • Initialise subscribers using snapshots or backup/restore.
  • The success window should appear when you finish.