fix: 대량 스캔 시 서버 사망 방지 — 세마포어 fast-fail + limit-concurrency 조정

- Alpaca intraday: 세마포어 대기 10초 제한, 초과 시 429 즉시 반환
  (기존: 120초 대기하며 커넥션 슬롯 점유 → 이벤트 루프 포화)
- Filing search: 세마포어(8) + 10초 fast-fail 추가
  (기존: 동시성 제한 없이 A-Z 스캔 시 수백 개 요청 쌓임)
- limit-concurrency 50→25 (실제 처리량은 세마포어가 제한하므로 여유 슬롯 불필요)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/api/v1/endpoints/alpaca.py

@@ -14,10 +14,12 @@ _ET = ZoneInfo("America/New_York")
 _MARKET_CLOSE_HOUR = 16  # 4:00 PM ET
 
 # Limit concurrent Alpaca intraday processing to prevent event-loop saturation
-# under bulk backfill workloads. Callers beyond this limit wait on the semaphore
+# under bulk backfill workloads.
-# (cheap asyncio wait) rather than flooding httpx connections and DB sessions.
-# Semaphore(5): BaseHTTPMiddleware removed → task count halved → safe to allow 5.
 _INTRADAY_SEMAPHORE = asyncio.Semaphore(5)
+# Max seconds a request waits for a semaphore slot before returning 429.
+# Prevents hundreds of requests piling up (each holding a connection slot)
+# during A-Z full-ticker scans.
+_SEMAPHORE_WAIT_TIMEOUT = 10
 
 
 def _market_closed_for(d: date) -> bool:
@@ -129,12 +131,21 @@ async def get_alpaca_intraday_multi(
     end_dt = datetime.combine(_end, datetime.max.time()).replace(tzinfo=timezone.utc)
 
     async def _do_fetch():
-        async with _INTRADAY_SEMAPHORE:
+        try:
+            await asyncio.wait_for(
+                _INTRADAY_SEMAPHORE.acquire(), timeout=_SEMAPHORE_WAIT_TIMEOUT
+            )
+        except asyncio.TimeoutError:
+            raise HTTPException(
+                status_code=429,
+                detail="서버가 바빠서 요청을 처리할 수 없습니다. 잠시 후 다시 시도하세요.",
+            )
         try:
             return await svc.get_or_fetch_multi_bars(
                 symbols, start_dt, end_dt, interval, force_refresh, feed="sip"
             )
         finally:
+            _INTRADAY_SEMAPHORE.release()
             try:
                 await svc.client.close()
             except Exception:
@@ -219,12 +230,21 @@ async def get_alpaca_intraday_today(
     end_dt = datetime.combine(today, datetime.max.time()).replace(tzinfo=timezone.utc)
 
     async def _do_fetch():
-        async with _INTRADAY_SEMAPHORE:
+        try:
+            await asyncio.wait_for(
+                _INTRADAY_SEMAPHORE.acquire(), timeout=_SEMAPHORE_WAIT_TIMEOUT
+            )
+        except asyncio.TimeoutError:
+            raise HTTPException(
+                status_code=429,
+                detail="서버가 바빠서 요청을 처리할 수 없습니다. 잠시 후 다시 시도하세요.",
+            )
         try:
             return await svc.get_or_fetch_multi_bars(
                 symbols, start_dt, end_dt, interval, force_refresh=True, feed="iex"
             )
         finally:
+            _INTRADAY_SEMAPHORE.release()
             try:
                 await svc.client.close()
             except Exception:

app/api/v1/endpoints/filings.py

@@ -37,6 +37,12 @@ from sqlalchemy import select, and_, func as sql_func
 router = APIRouter()
 logger = logging.getLogger("app.api.v1.filings")
 
+# Limit concurrent filing search requests to prevent event-loop saturation
+# during bulk A-Z ticker scans. Requests beyond this wait up to
+# _SEARCH_SEMAPHORE_TIMEOUT seconds, then fail fast with 429.
+_SEARCH_SEMAPHORE = asyncio.Semaphore(8)
+_SEARCH_SEMAPHORE_TIMEOUT = 10
+
 
 @router.get(
     "/search/{ticker}",
@@ -89,6 +95,18 @@ async def search_filings(
     except ValueError:
         raise HTTPException(status_code=400, detail="Invalid date format. Use YYYY-MM-DD")
 
+    # Fast-fail when server is overloaded (bulk A-Z scans)
+    try:
+        await asyncio.wait_for(
+            _SEARCH_SEMAPHORE.acquire(), timeout=_SEARCH_SEMAPHORE_TIMEOUT
+        )
+    except asyncio.TimeoutError:
+        raise HTTPException(
+            status_code=429,
+            detail="서버가 바빠서 요청을 처리할 수 없습니다. 잠시 후 다시 시도하세요.",
+        )
+
+    try:
         if force_refresh:
             try:
                 await sec_filings_service.index_filings(
@@ -120,6 +138,8 @@ async def search_filings(
         except Exception as e:
             logger.error(f"Filing search failed for {ticker}: {e}")
             raise HTTPException(status_code=502, detail=f"Filing search failed: {e}")
+    finally:
+        _SEARCH_SEMAPHORE.release()
 
     summaries = []
     for f in filings:

docker-compose.yml

@@ -68,7 +68,7 @@ services:
     mem_limit: 2g
     memswap_limit: 2g
     restart: unless-stopped
-    command: ["python", "-m", "uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "18000", "--reload", "--limit-concurrency", "50"]
+    command: ["python", "-m", "uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "18000", "--reload", "--limit-concurrency", "25"]
 
   # Frontend Application
   frontend: