feat(database): bound async configuration writes

app/db/engine.py

@@ -14,6 +14,7 @@ from sqlalchemy.pool import Pool
 
 from app.runtime.config import settings
 from app.db.diagnostics import _register_database_error_logging
+from app.db.worker import DATABASE_WORKER_MAX_WORKERS
 from app.runtime.log import logger
 from app.runtime.observability import record_metric
 
@@ -304,8 +305,8 @@ def connection_budget() -> Dict[str, int]:
     else:
         sync_max = settings.DB_SQLITE_POOL_SIZE + settings.DB_SQLITE_MAX_OVERFLOW
     if settings.DB_POOL_TYPE == "NullPool":
-        # 同步侧也可能被配成 NullPool，此时同样无界，用线程池规模作为可观测的上限估计
-        sync_max = settings.CONF.threadpool
+        # 未池化连接由通用线程池和专属数据库 worker 共同创建，二者都要计入上限估计。
+        sync_max = settings.CONF.threadpool + DATABASE_WORKER_MAX_WORKERS
     async_max = (settings.DB_ASYNC_POOL_SIZE + settings.DB_ASYNC_MAX_OVERFLOW
                  if _async_pool_enabled() else 0)
     fallback = settings.DB_ASYNC_FALLBACK_LIMIT if _async_pool_enabled() else settings.CONF.scheduler

app/db/worker.py

@@ -10,18 +10,17 @@ from contextvars import copy_context
 from dataclasses import dataclass
 from typing import Callable, TypeVar
 
+from app.application.database import (
+    DatabaseWorkerClosedError,
+    DatabaseWorkerOverloadedError,
+)
 from app.runtime.observability import record_metric
 
 
 T = TypeVar("T")
 
-
-class DatabaseWorkerClosedError(RuntimeError):
-    """数据库执行器尚未启动或已经停止。"""
-
-
-class DatabaseWorkerOverloadedError(RuntimeError):
-    """数据库执行器的运行与排队容量已经用尽。"""
+DATABASE_WORKER_MAX_WORKERS = 4
+DATABASE_WORKER_CAPACITY = 32
 
 
 @dataclass(frozen=True, slots=True)
@@ -47,7 +46,12 @@ class _WorkItem:
 class DatabaseWorker:
     """以有限线程和队列执行不能原生异步化的数据库短事务。"""
 
-    def __init__(self, *, max_workers: int = 4, capacity: int = 32) -> None:
+    def __init__(
+        self,
+        *,
+        max_workers: int = DATABASE_WORKER_MAX_WORKERS,
+        capacity: int = DATABASE_WORKER_CAPACITY,
+    ) -> None:
         """保存容量配置，线程只在显式启动后创建。"""
         if max_workers < 1:
             raise ValueError("数据库 worker 线程数必须大于 0")