fix: reduce mysql connection pressure

db/chat_log_db.py

@@ -20,9 +20,11 @@ _MYSQL_PASSWORD = os.getenv("MYSQL_PASSWORD", "")
 _MYSQL_DATABASE = os.getenv("MYSQL_DATABASE", "ai_cs")
 
 # ========== MySQL 连接池 ==========
-_POOL_SIZE = int(os.getenv("MYSQL_POOL_SIZE", "50"))
+_POOL_SIZE = int(os.getenv("MYSQL_POOL_SIZE", "10"))
+_POOL_WAIT_TIMEOUT = float(os.getenv("MYSQL_POOL_WAIT_TIMEOUT", "10"))
 _mysql_pool: Optional[Queue] = None
 _pool_lock = threading.Lock()
+_mysql_conn_count = 0
 
 
 def _create_mysql_conn():
@@ -44,58 +46,65 @@ def _create_mysql_conn():
 
 
 def _init_mysql_pool():
-    """初始化 MySQL 连接池"""
+    """初始化 MySQL 连接池（懒创建，不在启动时预建满）"""
     global _mysql_pool
     with _pool_lock:
         if _mysql_pool is None:
             _mysql_pool = Queue(maxsize=_POOL_SIZE)
-            for _ in range(_POOL_SIZE):
-                try:
-                    conn = _create_mysql_conn()
-                    _mysql_pool.put(conn)
-                except Exception:
-                    pass  # 启动时连接失败不阻塞，后续会重建
+
+
+def _discard_conn(conn):
+    """丢弃失效连接并维护计数"""
+    global _mysql_conn_count
+    try:
+        conn.close()
+    except Exception:
+        pass
+    with _pool_lock:
+        if _mysql_conn_count > 0:
+            _mysql_conn_count -= 1
 
 
 def _get_pooled_conn(timeout: float = 5.0):
-    """从连接池获取连接"""
-    global _mysql_pool
+    """从连接池获取连接，达到上限后阻塞等待，不再额外扩容。"""
+    global _mysql_pool, _mysql_conn_count
     if _mysql_pool is None:
         _init_mysql_pool()
-    
+
+    with _pool_lock:
+        if _mysql_conn_count < _POOL_SIZE:
+            conn = _create_mysql_conn()
+            _mysql_conn_count += 1
+            return conn
+
     try:
         conn = _mysql_pool.get(timeout=timeout)
-        # 检查连接是否有效
         try:
             conn.ping(reconnect=True)
         except Exception:
-            # 连接失效，创建新连接
-            try:
-                conn.close()
-            except Exception:
-                pass
-            conn = _create_mysql_conn()
+            _discard_conn(conn)
+            with _pool_lock:
+                if _mysql_conn_count < _POOL_SIZE:
+                    conn = _create_mysql_conn()
+                    _mysql_conn_count += 1
+                    return conn
+            conn = _mysql_pool.get(timeout=timeout)
+            conn.ping(reconnect=True)
         return conn
     except Empty:
-        # 池空了，创建新连接（不放回池）
-        return _create_mysql_conn()
+        raise TimeoutError(f"MySQL连接池已耗尽（pool_size={_POOL_SIZE}, wait_timeout={timeout}s）")
 
 
 def _return_conn(conn):
-    """归还连接到池"""
+    """归还连接到池，失效连接直接丢弃。"""
     global _mysql_pool
     if _mysql_pool is None:
         return
     try:
-        if _mysql_pool.qsize() < _POOL_SIZE:
-            _mysql_pool.put_nowait(conn)
-        else:
-            conn.close()
+        conn.ping(reconnect=False)
+        _mysql_pool.put_nowait(conn)
     except Exception:
-        try:
-            conn.close()
-        except Exception:
-            pass
+        _discard_conn(conn)
 
 
 class _CompatResult:
@@ -164,7 +173,7 @@ def _get_conn(max_retries: int = 3, retry_delay: float = 0.5) -> sqlite3.Connect
         last_error = None
         for attempt in range(max_retries):
             try:
-                conn = _get_pooled_conn(timeout=5.0)
+                conn = _get_pooled_conn(timeout=_POOL_WAIT_TIMEOUT)
                 return _PyMySQLCompatConn(conn, use_pool=True)
             except Exception as e:
                 last_error = e