Understanding RavenDB Architecture

Key Components

• Document Store: Central abstraction used by clients to interact with the database.
• Indexes: Automatically or manually created, indexes enable fast queries but require maintenance.
• Cluster Topology: RavenDB supports multi-node clusters with Raft consensus for high availability.

Operational Model

Each node can serve reads and writes. Indexing runs in the background. Replication and failover are handled internally, and clustering ensures data availability and consistency.

Common RavenDB Issues and Root Causes

1. Stale or Delayed Indexes

Indexes may lag behind writes under heavy load, large datasets, or when dealing with complex map-reduce logic. This can cause outdated query results unless explicitly requested to wait for non-stale results.

2. Document Conflicts in Replicated Clusters

When writes occur simultaneously across nodes during network partitions, conflicts can arise. Unresolved conflicts prevent consistent reads and must be manually resolved or automatically merged.

3. High Memory or CPU Usage

Large working sets or frequent indexing can spike memory and CPU. Misconfigured paging or batch sizes can exacerbate resource usage.

4. Replication Failures

Replication between nodes can break due to certificate mismatches, broken topology discovery, or node time skew. This results in data inconsistency and stale reads.

5. Cluster Instability or Node Drops

Nodes may be marked as passive or down due to heartbeat failure, firewall misconfiguration, or TLS issues. The Raft consensus algorithm will prevent failover until quorum is reestablished.

Diagnostics and Monitoring

Enable Traffic Watch

Use Traffic Watch from the Studio to monitor incoming requests, indexing operations, and errors in real time.

Review System Metrics

• Monitor Indexing Time, Document Writes, and Replication Queue.
• Use /admin/stats and /databases/<db>/stats REST endpoints for insights.

Check Index Health

Use the Studio or API to inspect index states. Look for "Faulty" or "Errored" statuses and check logs under Logs/.

Monitor Cluster Health

curl -X GET https://node-url:port/cluster/topology --cert cert.pfx:password

This confirms which nodes are in the cluster and their current roles.

Step-by-Step Remediation

1. Resolve Stale Indexes

Force queries to wait for non-stale results if necessary:

session.Advanced.WaitForNonStaleResults();

Also consider splitting complex indexes into smaller, more maintainable ones.

2. Auto-Merge Document Conflicts

Enable conflict resolution in the Studio:

• Go to Settings > Conflict Resolution
• Define resolution scripts or prefer latest/majority version

3. Tune Memory and Batch Sizes

DatabaseRecord.Settings["Raven/Queries/MaxPageSize"] = "512";
DatabaseRecord.Settings["Raven/Indexing/MaxMapAttempts"] = "3";

Apply via Studio or REST API for live tuning.

4. Fix Replication Connectivity

• Check cluster certificate expiration and renewal
• Verify correct DNS entries and firewall rules
• Ensure synchronized NTP across nodes

5. Reestablish Cluster Stability

Review Raft logs for split-brain conditions. Use:

curl -X GET https://node-url:port/admin/cluster/logs --cert cert.pfx:password

Promote passive nodes if quorum allows via Studio or Raft API.

Best Practices for RavenDB Stability

• Always run nodes behind a load balancer with sticky sessions
• Use HTTPS with valid certificates for all nodes
• Set WaitForNonStaleResults only where data consistency is critical
• Regularly backup and test restores using snapshot or export
• Implement alerting for index errors and replication delays

Conclusion

RavenDB delivers ACID-compliant NoSQL at scale, but managing it effectively requires a deep understanding of its indexing, clustering, and replication mechanics. From stale indexes to replication failures, production issues can degrade performance or data reliability if left unchecked. With the diagnostic techniques and remediation strategies provided in this guide, engineering teams can ensure their RavenDB clusters remain performant, consistent, and fault-tolerant.

FAQs

1. Why are my RavenDB queries returning stale data?

Because indexing is asynchronous by default. Use WaitForNonStaleResults() or optimize indexing throughput.

2. What causes document conflicts and how can I resolve them?

Conflicts arise from concurrent writes on separate nodes. Resolve via conflict resolution scripts or manual intervention in the Studio.

3. How do I detect slow indexes?

Monitor index performance metrics or check the Studio's index list for those marked as "Stale" or "Errored".

4. Can RavenDB clusters handle multi-region deployments?

Yes, but with added latency and potential for conflicts. Use delayed replication and robust conflict resolution policies.

5. How do I scale RavenDB safely?

Add nodes incrementally, monitor Raft quorum health, and ensure replication queues stay low during scaling operations.