{"id":14201,"date":"2023-03-22T15:02:44","date_gmt":"2023-03-22T22:02:44","guid":{"rendered":"https:\/\/www.couchbase.com\/blog\/?p=14201"},"modified":"2025-06-13T20:45:46","modified_gmt":"2025-06-14T03:45:46","slug":"couchbase-replication-and-sync","status":"publish","type":"post","link":"https:\/\/www.couchbase.com\/blog\/couchbase-replication-and-sync\/","title":{"rendered":"Data Replication and Synchronization in Couchbase"},"content":{"rendered":"

Data replication and synchronization may seem redundant at first glance. They both refer to copying data from one persistent repository to another for consistency in a distributed architecture. But for Couchbase, each term has a different meaning and each is used for different purposes.<\/span><\/p>\n

This post is an overview of Couchbase Cross Datacenter Replication (XDCR), which provides data replication between database clusters, and Couchbase Sync Gateway\/Capella App Services, which enables data synchronization for mobile, IoT and edge applications.<\/span><\/p>\n

Cross Datacenter Replication (XDCR)<\/span><\/h2>\n

XDCR Overview<\/span><\/h3>\n

Couchbase’s <\/span>Cross Datacenter Replication (XDCR)<\/span><\/a> enables the replication of data across clusters located in different datacenters. Inter-cluster replication is used to ensure even distribution and high availability of data. The protocol used for XDCR is called DCP (data change protocol). DCP is also used for inter-cluster replication and, in both cases, is used for low-latency memory-to-memory replication.<\/span><\/p>\n

XDCR is designed for global replication: replicating data between multiple regions, multiple datacenters, multiple cloud providers, or any combination. Multiple clusters are needed if you want to replicate data across different regions. Unlike other databases, Couchbase’s multi-datacenter functionality is not provided by stretching a single cluster across multiple datacenters. Due to high network latencies, nodes\/servers in different regions cannot be part of the same cluster. Each cluster is independent.<\/span><\/p>\n

XDCR can be very simple to start with, but many powerful features and options are available. It supports unidirectional and bidirectional operation and active-active replication with automatic conflict resolution. Use filtered replication for replicating subsets of documents.<\/span><\/p>\n

XDCR Nuts and Bolts<\/span><\/h3>\n

XDCR replicates data from a <\/span>source<\/span><\/i> bucket to a <\/span>target<\/span><\/i> bucket (XDCR also supports scope\/collection replication, both implicit and explicit). Replication is from memory to memory and asynchronous, and both existing and modified data are replicated.\u00a0<\/span><\/p>\n

Multiple data streams are shuffled across all shards (vBuckets) to move data in parallel to the destination cluster for additional latency reduction.<\/span><\/p>\n

Source and destination clusters can have different numbers of servers (nodes), and XDCR is resilient to topology changes.<\/span><\/p>\n

XDCR Use cases<\/span><\/h3>\n

Unidirectional (one-way) and bidirectional (two-way) configurations each have their own use cases.<\/span><\/p>\n

Unidirectional Replication<\/span><\/h4>\n

One-way replication is great for:<\/span><\/p>\n

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  • \n
      \n
    • Disaster Recovery<\/b> – Latest data is always available in the event of a disaster. This enables quick failover and recovery without loss of data or downtime.<\/span><\/li>\n
    • Dev\/test copies<\/b> – Provision copies of production data for testing and development purposes. This reduces the need for manual data copying and reduces the risk of errors or inconsistencies between the environments. XDCR provides near real-time replication, meaning that test data is always up-to-date with production data.<\/span><\/li>\n
    • Reporting\/Archival<\/b> – Replicating data to a dedicated reporting or archival cluster allows for efficient reporting and analysis without impacting the performance of the production environment. XDCR enables real-time or near real-time replication of data, so reporting or archival cluster is always up-to-date with the latest data. This makes it a solution for organizations that need to maintain historical data for compliance or analysis purposes.<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n

      Bidirectional Replication<\/span><\/h4>\n

      Two-way replication can be used for use cases such as:<\/span><\/p>\n

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      • \n
          \n
        • Multiple “hot” active clusters –<\/b> By replicating data across multiple datacenters, XDCR can help provide efficient load balancing and high data availability. XDCR enables real-time or near-real-time data replication, ensuring all active clusters are always in sync. Suitable for organizations that need to serve large volumes of traffic or have a globally distributed user base.<\/span><\/li>\n
        • Data locality –<\/b> With XDCR, you can create geographically distributed clusters, allowing data to be stored closer to the users and reducing latency. XDCR can automatically replicate data across multiple datacenters, ensuring that data is always up-to-date at the nearest location.<\/span><\/li>\n
        • Geofencing – <\/b>XDCR can be configured to replicate certain data only to specific clusters, ensuring that data is only available within designated geographic regions. This can be used by organizations that must comply with data privacy regulations or enforce geofencing restrictions on their data.<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n

          XDCR Options<\/span><\/h3>\n

          Conflict resolution<\/b> resolves conflicts that arise when different nodes in the cluster attempt to update the same data simultaneously. Sequence-based conflict resolution resolves conflicts based on the order in which updates are received. In contrast, timestamp-based conflict resolution uses the timestamp of the updates to determine which update is more recent and should be applied. Depending on the specific use case, one type of conflict resolution may be more appropriate, and Couchbase’s XDCR allows for flexibility in choosing the appropriate method.<\/span><\/p>\n

          Filtering<\/b> allows users to specify which documents should be included or excluded from replication between clusters. This can be based on criteria such as document type, attribute values, or other metadata. XDCR filtering provides greater control over which documents are replicated, reducing the amount of unnecessary network traffic and storage overhead while improving replication efficiency and overall system performance.<\/span><\/p>\n

          Document deletion<\/b> in one cluster will trigger the deletion of the corresponding document in the other cluster. However, this behavior can be filtered, allowing organizations to maintain historical data for archival or reporting use cases. By filtering out document deletions, organizations can ensure that data remains available in their reporting or archival clusters, even if the corresponding documents have been deleted in the production cluster. This can help organizations comply with data retention policies and ensure that important data is always available for analysis and reporting.<\/span><\/p>\n

          XDCR can also support migration scenarios, such as infrastructure-agnostic migration from on-prem to the cloud.<\/span><\/p>\n

          XDCR Summary<\/span><\/h3>\n

          Couchbase’s XDCR feature is one of the primary features that first attracts Couchbase customers and users. It’s a simple and flexible tool for replicating data across different clusters located in different datacenters.<\/span><\/p>\n

          The following table lists the primary use cases for XDCR in a Couchbase Server or Couchbase Capella deployment:<\/span><\/p>\n\n\n\n\n\n\n\n\n\n
          \n

          XDCR<\/b><\/p>\n<\/td>\n<\/tr>\n

          Disaster recovery<\/span><\/td>\n<\/tr>\n
          Dev\/Test Copies<\/span><\/td>\n<\/tr>\n
          Reporting, auditing, archival<\/span><\/td>\n<\/tr>\n
          Datacenter locality<\/span><\/td>\n<\/tr>\n
          Geo-fencing<\/span><\/td>\n<\/tr>\n
          Cloud data migration<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

          See a live demo of Couchbase XDCR in action<\/a>, below:<\/span><\/p>\n