altinity Memory Usage and OOM Diagnostics
Diagnose RAM usage, memory pressure, OOM risks, and memory allocation patterns.
Diagnostics
Run all queries from checks.sql in this skill's directory and analyze the results.
Problem Investigation
High Memory from Aggregations
Solutions:
- Add
max_bytes_before_external_group_by - Use
max_threadspragma to limit parallelism - Restructure query to reduce group by cardinality
High Memory from JOINs
Solutions:
- Use
max_bytes_in_join - Consider
join_algorithm = 'partial_merge'or'auto' - Ensure smaller table on right side
Ad-Hoc Query Guidelines
Required Safeguards
-- Always time-bound log queries
where event_date >= today() - 1
-- Limit results
limit 100
Memory-Related Metrics
MemoryTracking- current tracked memoryMemoryResident- RSSOSMemoryTotal,OSMemoryFreeWithoutCached- system memory
Cross-Module Triggers
| Finding | Load Module | Reason |
|---|---|---|
| High merge memory | altinity-expert-clickhouse-merges |
Analyze merge patterns |
| Large dictionaries | altinity-expert-clickhouse-dictionaries |
Dictionary optimization |
| Cache too large | altinity-expert-clickhouse-caches |
Cache sizing |
| PK memory high | altinity-expert-clickhouse-schema |
ORDER BY optimization |
| Query OOMs | altinity-expert-clickhouse-reporting |
Query optimization |
Settings Reference
| Setting | Scope | Notes |
|---|---|---|
max_memory_usage |
Query | Per-query limit |
max_memory_usage_for_user |
User | Per-user aggregate |
max_server_memory_usage |
Server | Global limit |
max_server_memory_usage_to_ram_ratio |
Server | Auto-limit as % of RAM |
max_bytes_before_external_group_by |
Query | Spill aggregation to disk |
max_bytes_in_join |
Query | Spill join to disk |