ClickHouse

Memory Pressure and OOM Risk

critical
Resource ContentionUpdated Feb 6, 2026

Memory usage approaching system limits can cause query failures, crashes, or degraded performance, especially during large aggregations or joins.

Sources
Common issues you can solve using advanced monitoring ...clickhouse.com
Ignite ClickHouse Alerts: Detect Performance Issues Earlychistadata.com
How to Monitor ClickHouse Query Performance with OpenTelemetryoneuptime.com
Technologies:
ClickHouseSymptoms of this issue are visible in ClickHouse metrics and logs
clickhouse.memory.tracking
clickhouse.memory.tracking_for_merges
How to detect:

Monitor MemoryTracking and MemoryTrackingForMerges from system.metrics. Alert when memory usage exceeds 80% of available memory or when MemoryTrackingForMerges is consistently high.

Recommended action:

Review query memory usage from system.query_log, adjust max_memory_usage settings, optimize queries with high memory consumption, tune merge settings to reduce concurrent merge memory usage, or scale vertically with more RAM.