Bidirectional transactional replication in SQL Server enables two databases to exchange changes with each other in near real time. Enterprise IT and data engineering teams use this approach to support active-active architectures, distribute read and write workloads, and improve resilience for mission critical systems. This guide explains how to plan, configure, monitor, and operate bidirectional transactional replication in SQL Server, while also showing how CData Sync simplifies complex replication scenarios at scale.
Understanding bidirectional transactional replication in SQL Server
Bidirectional transactional replication lets two servers exchange changes by publishing and subscribing to each other’s data. Each SQL Server instance acts as both a publisher and a subscriber, which allows updates on either side to propagate to the other.
This topology supports active-active environments where applications can read and write to either server. Teams often deploy it for load balancing, regional distribution, and disaster recovery scenarios where both databases must remain operational.
It is important to distinguish bidirectional transactional replication from peer to peer replication. Peer to peer replication offers built in multi node active-active behaviour, but it requires SQL Server Enterprise Edition. Bidirectional transactional replication works on Standard Edition and above, but it demands careful planning, loop prevention, and conflict management.
Replication topology comparison
Feature | Unidirectional | Bidirectional | Peer to peer |
Data flow | One way | Two ways | Multi node |
Active-active support | No | Yes | Yes |
Edition requirement | Standard | Standard and above | Enterprise only |
Conflict handling | Minimal | Manual planning required | Built in |
Typical use cases | Reporting, ETL | Load balancing, DR | Large scale distributed systems |
Preparing for bidirectional replication setup
Preparation determines success in bidirectional transactional replication. Teams should treat prerequisites as mandatory steps and integrate them into standard operating procedures for database changes.
Synchronize database schemas and primary keys
Both databases must start with identical schemas and primary keys. This includes tables, columns, indexes, constraints, and data types.
A primary key in SQL Server uniquely identifies each row in a table. Transactional replication relies on primary keys and unique indexes to track and apply changes accurately.
Identity columns often introduce conflicts. Plan identity ranges carefully and mark identity columns as NOT FOR REPLICATION where appropriate. This setting prevents SQL Server from automatically incrementing identity values during replication and reduces duplicate key errors.
Verify server names and network connectivity
Each SQL Server instance must report a consistent and correct server name. Run @@SERVERNAME on each instance and confirm it returns the fully qualified domain name.
Ensure reliable network connectivity between servers. Open required ports such as TCP 1433 and confirm firewall rules allow bidirectional traffic.
Confirm edition and security requirements
Bidirectional transactional replication works on SQL Server Standard Edition and above while Peer to peer replication requires Enterprise Edition.
The SQL Server Agent account runs replication agents such as the Snapshot Agent, Log Reader Agent, and Distribution Agent. This account needs appropriate SQL permissions, file system access, and network visibility.
Maintain a security matrix that documents agent accounts, folder permissions such as repldata, and database roles. Align this matrix with corporate security policies to simplify audits and troubleshooting.
Native SQL Server bidirectional replication
Native SQL Server transactional replication provides granular control and tight integration with SQL Server Management Studio. This section outlines the high-level configuration flow.
Configuring distributors and publishers
In bidirectional replication, each server acts as both a publisher and a distributor. The distributor manages replication metadata and coordinates data movement between publishers and subscribers.
Plan the topology so each server publishes its local changes and subscribes to changes from the other server. A simple diagram or checklist often helps teams visualize cross publishing relationships.
Setting up the distributor role
Configure the distributor role using SQL Server Management Studio. Choose a local or remote distributor, but many bidirectional setups use a local distributor on each server.
Transactional replication requires the Snapshot Agent, Log Reader Agent, and Distribution Agent. Plan snapshot and distribution folders carefully, as both servers must access these locations.
Enabling publications on both servers
Create a publication on each server for the tables and objects that require replication. Use SQL Server Management Studio to define transactional publications and select articles.
Prepare a clear list of tables that need replication and validate them against data governance standards. Avoid publishing unnecessary or reference only tables unless required.
Defining and managing articles
Articles define the specific tables and objects included in a publication. Both servers must publish the same set of articles for symmetry and predictable behaviour.
Ensure every article has a primary key or suitable unique index. Replication agents depend on these keys to identify rows during inserts, updates, and deletes.
Many teams use an internal template or checklist to confirm article definitions match exactly across servers.
Establishing bidirectional publications
Native bidirectional replication differs from peer to peer replication. SQL Server does not automatically manage multi node conflict resolution in Standard Edition scenarios.
Manual bidirectional transactional replication requires careful loop prevention and conflict planning. Peer to peer replication, which is Enterprise only, simplifies this with built in active-active behaviour.
Adding subscriptions with loopback detection
When adding subscriptions, enable loopback detection. Set @loopback_detection = TRUE so changes delivered to a subscriber do not get republished back to the origin.
Loopback detection prevents infinite replication cycles where the same change bounces between servers. It works by ignoring changes that originate from the replication partner.
Granting permissions to SQL Server Agent accounts
Grant each SQL Server Agent account access to the other server’s repldata folder so replication agents can read and write snapshot and distribution files.
Add the relevant accounts to the Publication Access List in SQL Server Management Studio. Permission issues often cause silent replication failures or stalled agents.
Initializing and validating replication
Transactional replication starts with a snapshot of existing data and then mirrors subsequent changes through replication agents.
If zero downtime is mandatory, pre seed identical data on both servers before initializing subscriptions. This approach reduces snapshot time and production impact.
Use Replication Monitor or the View Synchronization Status option in SQL Server Management Studio to confirm successful initialization and ongoing health.
Monitoring and maintaining bidirectional replication
Bidirectional replication requires ongoing attention to maintain data integrity and performance.
Track metrics such as replication lag, synchronization status, and data drift. Use SQL Server Replication Monitor for native visibility and consider third party dashboards for centralized monitoring. Validate data integrity periodically using row counts, checksums, or reconciliation queries.
Test conflict scenarios in non-production environments and document recovery procedures, including reinitialization steps.
Using CData Sync for bidirectional SQL Server replication
Native SQL Server replication offers powerful features but can become complex to manage at scale. CData Sync provides an alternative approach that simplifies bidirectional replication using independent, change based jobs with centralized governance.
CData positions itself as a secure, compliant, and AI enhanced replication partner for enterprises that need predictable, high-volume synchronization across heterogeneous environments.
Configure connections
Add a connection for each SQL Server instance in CData Sync. Validate credentials, network connectivity, and schema visibility during setup.
Ensure primary keys exist on replicated tables, as CData Sync relies on them for incremental change tracking.
Configure bidirectional replication jobs
CData Sync implements bidirectional replication using two independent jobs.
Create the first job to replicate data from Server A to Server B. Create the second job to replicate data from Server B to Server A. Both jobs must run to achieve bidirectional synchronization. Each job handles a single replication direction, which simplifies troubleshooting and scheduling. Select tables for each job and confirm the keys used for change detection. Schedule jobs or run them continuously based on latency and workload requirements.
Configure change capture behaviour
CData Sync identifies incremental changes using SQL Server change tracking or Change Data Capture where available.
Enable incremental replication to reduce load and avoid full refreshes. Keep change capture settings consistent across both replication directions to minimize conflict risk.
Configure optional transformations and controls
CData Sync supports filters, mappings, and transformations that improve governance and reduce conflicts.
Apply table or column filters to limit replicated data. Use column mappings or transformations when schemas differ. Exclude non-operational or reference data when appropriate.
Monitor job runs, errors, and synchronization status centrally in the CData Sync console, which simplifies operations for distributed teams.
Troubleshooting common issues in bidirectional replication
Bidirectional replication introduces additional complexity compared to unidirectional setups.
Common issues include subscriptions not appearing, agent timeouts, permission errors, and primary key or FQDN mismatches. Review server names, security settings, and agent job histories when troubleshooting.
Master-master replication requires orchestration. Without careful planning, conflicts can occur and impact data integrity.
Frequently Asked Questions
What are the key prerequisites for bidirectional transactional replication?
To configure bidirectional transactional replication, ensure both servers use compatible SQL Server editions, have identical schemas and primary keys, and are properly networked with open ports and configured security permissions.
How do I prevent conflicts with identity columns in bidirectional replication?
Mark identity columns as NOT FOR REPLICATION and partition ranges or use surrogate keys to minimize the risk of conflicts and data duplication during bidirectional synchronization.
How can I handle replication latency and agent errors?
Monitor replication lag via Replication Monitor and extend agent job timeouts as needed; resolve agent errors by confirming network connectivity, permissions, and agent status.
Is bidirectional transactional replication supported in cloud managed SQL Server instances?
Bidirectional transactional replication is supported with Azure SQL Managed Instance if networking and required ports are configured properly.
What steps should I follow to test bidirectional replication effectively?
Perform insert, update, and delete operations on both servers and verify that changes are reflected correctly on the other server.
Build secure, scalable bidirectional SQL Server replication with CData Sync
Bidirectional transactional replication enables active-active SQL Server architectures that support high availability and operational scale, but complexity without governance introduces risk.
CData Sync provides a secure, scalable foundation for predictable bidirectional SQL Server replication, helping enterprises synchronize data in real time while maintaining control, compliance, and operational simplicity. Start a free 14 day trial today.
