altinity-expert-clickhouse-replication

Diagnose ClickHouse replication lag and readonly replicas by querying system.replicas and system.replication_queue to surface health metrics, identify root causes, and recommend actionable fixes for stalled replication tasks.

A ClickHouse replica becomes readonly or experiences high lag due to replication queue backlogs and Keeper connectivity issues. Inspecting system.zookeeper_connection and system.replication_queue identifies stalled tasks, session errors, and failover readiness problems.

Check ClickHouse Keeper connectivity and session status by querying the system.zookeeper_connection table to verify quorum stability, monitor recent session errors, and ensure replication health diagnostics accurately reflect underlying coordination service issues.

Fix a stalled ClickHouse replication queue by inspecting system.replication_queue metrics to prioritize remediation of stuck tasks. Analyzing queue sizes and replica lag locates root causes and applies actionable fixes to restore normal replication.

Run ClickHouse replication health diagnostics when clusters experience silent failures, data divergence, readonly replicas, or significant backlog in replication tasks. Evaluating failover readiness and Keeper connections prevents severe replication issues across distributed environments.