fix: 修復 Worker 退出時執行緒卡住導致 timeout 問題

- 增加 graceful_timeout 從 10s 到 30s，給予執行緒足夠清理時間
- worker_exit hook 新增停止背景同步執行緒邏輯
- 調整 SLOW_QUERY_THRESHOLD 預設值為 5.0s (即時視圖查詢通常需 2-5s)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.env.example

@@ -112,8 +112,9 @@ CIRCUIT_BREAKER_WINDOW_SIZE=10
 # ============================================================
 # Performance Metrics Configuration
 # ============================================================
-# Slow query threshold in seconds (default: 1.0)
-SLOW_QUERY_THRESHOLD=1.0
+# Slow query threshold in seconds (default: 5.0)
+# Note: Real-time Oracle views may take 2-5s per query, set threshold accordingly
+SLOW_QUERY_THRESHOLD=5.0
 
 # ============================================================
 # SQLite Log Store Configuration

gunicorn.conf.py

@@ -7,7 +7,7 @@ worker_class = "gthread"
 
 # Timeout settings - critical for dashboard stability
 timeout = 65          # Worker timeout: must be > call_timeout (55s)
-graceful_timeout = 10 # Graceful shutdown timeout (reduced for faster restart)
+graceful_timeout = 30 # Graceful shutdown timeout (enough for thread cleanup)
 keepalive = 5         # Keep-alive connections timeout
 
 # Worker lifecycle management - prevent state accumulation
@@ -20,7 +20,17 @@ max_requests_jitter = 100 # Random jitter to prevent simultaneous restarts
 # ============================================================
 
 def worker_exit(server, worker):
-    """Clean up database connections when worker exits."""
+    """Clean up background threads and database connections when worker exits."""
+    # Stop background sync threads first
+    try:
+        from mes_dashboard.services.realtime_equipment_cache import (
+            stop_equipment_status_sync_worker
+        )
+        stop_equipment_status_sync_worker()
+    except Exception as e:
+        server.log.warning(f"Error stopping equipment sync worker: {e}")
+
+    # Then dispose database connections
     try:
         from mes_dashboard.core.database import dispose_engine
         dispose_engine()