diff --git a/backend/backfill_agg_trades.py b/backend/backfill_agg_trades.py
index 89d2223..1381e5c 100644
--- a/backend/backfill_agg_trades.py
+++ b/backend/backfill_agg_trades.py
@@ -37,7 +37,7 @@ DB_PATH = os.path.join(os.path.dirname(__file__), "..", "arb.db")
 BINANCE_FAPI = "https://fapi.binance.com/fapi/v1"
 HEADERS = {"User-Agent": "Mozilla/5.0 ArbitrageEngine/backfill"}
 BATCH_SIZE = 1000
-SLEEP_MS = 200  # 毫秒/请求
+SLEEP_MS = 2000  # 低优先级：2秒/请求，让出锁给实时服务
 
 
 # ─── DB helpers ──────────────────────────────────────────────────