ngx_http_monitoring_module/docs/PERFORMANCE.md

Performance

Hot Path

The log-phase request accounting path performs:

• one timestamp delta calculation
• atomic increments for request, status, method, latency, and size buckets
• one bounded top-URL table update
• optional user-agent and upstream updates

Top-N table insertion or replacement takes the shared slab mutex, but existing entries update with atomics only.

Collector Cost

Collectors run from Nginx timers at monitor_refresh_interval. API requests do not trigger collection. Default collection is once per second.

For very large hosts, /proc/net/tcp and /proc/net/tcp6 can be expensive because they scale with connection count. If needed, increase monitor_refresh_interval or disable system collection:

monitor_collect_system off;

Memory

Default shared memory is 8 MiB:

monitor_shm_size 8m;

The default fixed-size structures are bounded:

• history samples: 3600 maximum
• top URLs: 256 maximum
• user agents: 64 maximum
• upstream peers: 128 maximum
• workers: 128 maximum
• interfaces, disks, filesystems: 32 each

Operational Guidance

• Build with --with-compat.
• Build with --with-http_stub_status_module for exact Nginx connection counters.
• Keep dashboard access private with monitor_allow / monitor_deny or standard Nginx auth modules.
• Use monitor_api_token when exposing API or SSE across trust boundaries.
• Put /monitor behind an internal listener or VPN for production.
• Keep monitor_resolution at 1s or higher on very busy systems.