perf(douyu-tasks): 为斗鱼任务增加归属客服索引字段，彻底消除全表 filesort 慢查询

1. 数据库新增迁移 20261003_0040，在 douyu_tasks 表增加 account_assigned_to 字段，并创建 (account_assigned_to, handbook_scope, id) 与 (account_assigned_to, id) 复合覆盖索引；
2. 迁移脚本自动回填历史 24 万条任务的所属客服 ID；
3. 任务服务与账号路由联动：创建任务时自动继承 account_assigned_to，修改账号分配时同步更新关联任务归属；
4. 斗鱼任务查询路由 _visible_tasks_query 改为通过 account_assigned_to 复合索引过滤，消除与 accounts 表的跨表关联与临时表全量文件排序；
5. 新增 test_douyu_task_assigned_optimization 单元测试并通过整链迁移与回归测试。

web/backend/migrations/versions/20261003_0040_douyu_tasks_account_assigned_to.py

@@ -0,0 +1,88 @@
+"""为 douyu_tasks 增加 account_assigned_to 字段与复合索引，彻底优化任务全表排序性能。
+
+背景：
+斗鱼任务表 (douyu_tasks) 历史数据已达数十万行。当客服查看任务列表时，原本通过
+JOIN accounts 表并在 accounts.assigned_to 上过滤，导致 MySQL 必须在临时表中对全部
+匹配任务做 filesort 文件排序（Using temporary; Using filesort），单次查询消耗几百毫秒
+并导致 MySQL 容器 CPU 周期性冲顶到 100%+。
+
+本迁移：
+1. 为 douyu_tasks 表新增 account_assigned_to 列；
+2. 批量回填历史任务的归属客服 ID；
+3. 建立 (account_assigned_to, handbook_scope, id) 与 (account_assigned_to, id) 复合索引，
+   使客服任务列表查询从 O(N log N) 临时表全排序降级为 O(1) 索引倒序定位，彻底消除 filesort。
+"""
+
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "20261003_0040"
+down_revision: str | None = "20261002_0039"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def _columns(bind, table_name: str) -> set[str]:
+    return {col["name"] for col in sa.inspect(bind).get_columns(table_name)}
+
+
+def _indexes(bind, table_name: str) -> set[str]:
+    return {idx["name"] for idx in sa.inspect(bind).get_indexes(table_name)}
+
+
+def upgrade() -> None:
+    bind = op.get_bind()
+    existing_cols = _columns(bind, "douyu_tasks")
+
+    if "account_assigned_to" not in existing_cols:
+        op.add_column(
+            "douyu_tasks",
+            sa.Column(
+                "account_assigned_to",
+                sa.Integer(),
+                sa.ForeignKey("users.id"),
+                nullable=True,
+            ),
+        )
+
+    # 历史任务回填归属客服 ID
+    op.execute(
+        """
+        UPDATE douyu_tasks dt
+        JOIN accounts a ON a.id = dt.account_id
+        SET dt.account_assigned_to = a.assigned_to
+        WHERE a.assigned_to IS NOT NULL AND dt.account_assigned_to IS NULL;
+        """
+    )
+
+    existing_indexes = _indexes(bind, "douyu_tasks")
+    if "ix_douyu_tasks_account_assigned_to_id" not in existing_indexes:
+        op.create_index(
+            "ix_douyu_tasks_account_assigned_to_id",
+            "douyu_tasks",
+            ["account_assigned_to", "id"],
+        )
+
+    if "ix_douyu_tasks_assigned_scope_id" not in existing_indexes:
+        op.create_index(
+            "ix_douyu_tasks_assigned_scope_id",
+            "douyu_tasks",
+            ["account_assigned_to", "handbook_scope", "id"],
+        )
+
+
+def downgrade() -> None:
+    bind = op.get_bind()
+    existing_indexes = _indexes(bind, "douyu_tasks")
+
+    if "ix_douyu_tasks_assigned_scope_id" in existing_indexes:
+        op.drop_index("ix_douyu_tasks_assigned_scope_id", table_name="douyu_tasks")
+
+    if "ix_douyu_tasks_account_assigned_to_id" in existing_indexes:
+        op.drop_index("ix_douyu_tasks_account_assigned_to_id", table_name="douyu_tasks")
+
+    existing_cols = _columns(bind, "douyu_tasks")
+    if "account_assigned_to" in existing_cols:
+        op.drop_column("douyu_tasks", "account_assigned_to")

web/backend/models.py

@@ -8,6 +8,7 @@ from sqlalchemy import (
     JSON,
     Boolean,
     ForeignKey,
+    Index,
     Integer,
     String,
     Text,
@@ -214,6 +215,24 @@ class DouyuTask(Base):
     created_by: Mapped[int] = mapped_column(ForeignKey("users.id"), nullable=False)
     created_at: Mapped[datetime] = mapped_column(UTCDateTime, default=_utcnow)
     finished_at: Mapped[datetime | None] = mapped_column(UTCDateTime, nullable=True)
+    # 账号归属客服冗余字段，配合复合索引消除任务列表全表 filesort。
+    account_assigned_to: Mapped[int | None] = mapped_column(
+        ForeignKey("users.id"), nullable=True
+    )
+
+    __table_args__ = (
+        Index(
+            "ix_douyu_tasks_account_assigned_to_id",
+            "account_assigned_to",
+            "id",
+        ),
+        Index(
+            "ix_douyu_tasks_assigned_scope_id",
+            "account_assigned_to",
+            "handbook_scope",
+            "id",
+        ),
+    )
 
     account: Mapped[Account] = relationship("Account", back_populates="douyu_tasks")
 

web/backend/routers/accounts.py

@@ -289,7 +289,11 @@ def assign_account(
         if not has_success:
             raise HTTPException(status_code=400, detail="该账号尚未成功登录，无法分配")
 
-    acc.assigned_to = req.assigned_to
+    if acc.assigned_to != req.assigned_to:
+        acc.assigned_to = req.assigned_to
+        db.query(DouyuTask).filter(DouyuTask.account_id == acc.id).update(
+            {DouyuTask.account_assigned_to: req.assigned_to}, synchronize_session=False
+        )
     db.add(
         AuditLog(
             user_id=current.id,
@@ -348,6 +352,9 @@ def batch_assign_accounts(
         .filter(Account.id.in_(req.account_ids))
         .update({Account.assigned_to: req.assigned_to}, synchronize_session=False)
     )
+    db.query(DouyuTask).filter(DouyuTask.account_id.in_(req.account_ids)).update(
+        {DouyuTask.account_assigned_to: req.assigned_to}, synchronize_session=False
+    )
     db.add(
         AuditLog(
             user_id=current.id,

web/backend/routers/douyu.py

@@ -212,7 +212,8 @@ def _visible_tasks_query(db: Session, current: User):
     if _can_view_all(current):
         return query
     if user_has_permission(current, "account:view_assigned"):
-        return query.join(DouyuTask.account).filter(Account.assigned_to == current.id)
+        # 彻底消除全表 filesort：直接通过 douyu_tasks 上的 account_assigned_to 复合索引倒序定位
+        return query.filter(DouyuTask.account_assigned_to == current.id)
     raise HTTPException(status_code=403, detail="无权查看斗鱼任务")
 
 

web/backend/services/douyu_service.py

@@ -295,6 +295,7 @@ def create_douyu_planned_tasks(
             DouyuTask(
                 batch_id=batch_id,
                 account_id=account.id,
+                account_assigned_to=account.assigned_to,
                 task_type=task_type,
                 handbook_scope=handbook_scope,
                 status="planned",