FLIN App

Memory

RSS Gauge

DB Size

WAL + Data Files

Uptime

Since Server Start

Auto-Refresh

What's Monitored

Six key metrics collected with zero-cost atomics — no external monitoring agent needed.

Memory Monitoring

Tracks the server process RSS (Resident Set Size) in megabytes. Displayed as a real-time gauge on the dashboard.

Database Size

Reports the total size of .flindb/ including WAL files, per-entity data files, and backup snapshots.

Request Counters

Total requests served since server start. Tracked via AtomicU64 — no mutex overhead, no performance impact.

Response Time Tracking

Average response time in microseconds across all requests. Helps identify performance regressions instantly.

Error Rate

Total errors and error percentage. A spike in the error rate signals problems before users start complaining.

Auto-Refresh (5s)

The metrics dashboard refreshes every 5 seconds. No manual reloading — just leave it open and watch.

How It Works

Metrics are collected per-request with zero-cost atomic operations. No sampling, no approximation.

Metrics Collection

For every incoming request:
─────────────────────────────────────────

1. Instant::now()          → Start timer
2. Handle request          → Route, render, respond
3. record_request()        → Atomically update:
   ├── TOTAL_REQUESTS      → AtomicU64::fetch_add(1)
   ├── TOTAL_ERRORS        → +1 if status >= 400
   ├── TOTAL_RESPONSE_TIME → +elapsed microseconds
   ├── ROUTE_STATS         → Per-route counters
   └── STATUS_COUNTS       → Per-status-code counters

No mutex. No lock contention. No overhead.
Admin routes (/_flin/*) excluded from aggregates.

API Endpoint

A single endpoint returns all system metrics at once.

Method	Endpoint	Description
GET	`/_flin/api/metrics`	Returns memory, database, uptime, request, and error metrics

Example Response

GET /_flin/api/metrics

{
  "memory_mb": 24.5,
  "db_size_bytes": 1048576,
  "uptime_seconds": 3600,
  "total_requests": 12847,
  "total_errors": 23,
  "avg_response_time_us": 1250
}

Zero-Cost Monitoring

All metrics are collected with AtomicU64 counters — no external monitoring agent, no performance overhead, no configuration. The metrics dashboard works from the first request. Leave it open during development, use it for production health checks.

FLIN vs. Traditional Stacks

Traditional Stack

Install Prometheus for metrics collection and alerting
Set up Grafana for visualization and dashboards
Configure StatsD or custom middleware for request timing
Deploy a separate monitoring agent on each server
Manage metric retention policies and storage costs

FLIN

Metrics collected per-request with zero configuration
Real-time dashboard with auto-refresh built in
Memory, DB, uptime, requests, errors — all in one view
Atomic counters with no lock contention or overhead
Works in development and production identically

System Metrics