xamxam/todo/03-system-cache.md

System Page Caching — Database-Backed Status Cache

Problem

The admin system page (/admin/system.php) runs expensive operations on every load:

• systemctl subprocess calls (~4 checks × ~100ms each)
• curl HTTP self-check (~200-500ms)
• disk_total_space()/disk_free_space() (fast but unnecessary per-request)
• Log file tail + filesize + filemtime (I/O bound)
• Nginx config file reading

Solution: system_cache table + background refresh

• Add system_cache table to schema: CREATE TABLE system_cache (key TEXT PRIMARY KEY, value TEXT NOT NULL, updated_at INTEGER NOT NULL)
• Add migration storage/migrations/007_system_cache.sql
• Add SystemCache class (src/SystemCache.php) with methods:
  • get(string $key, int $maxAgeSec = 60): ?array
  • set(string $key, array $data): void
  • isStale(string $key, int $maxAgeSec = 60): bool
• Refactor system.php status section:
  1. Check SystemCache::get('system_status', 120) — 2-minute TTL
  2. If cache hit → render from cache, show "mis en cache il y a X sec" label
  3. If cache miss → run checks, store in cache, render
  4. Add ?refresh=1 GET param to force-bypass cache
• Refactor system.php log sections — avoid re-reading on every tab switch; only read the active tab's log
• Cache disk info separately with 5-minute TTL: SystemCache::get('disk_info', 300)
• Cache PHP info separately with 1-hour TTL: SystemCache::get('php_info', 3600)