Scraper: process-wide lock, one scrape at a time

Concurrent manual scrapes were interleaving (two Chromium sessions on one
LXC) causing the page timeouts behind partial results. SCRAPE_LOCK guards
run_manual_scrape and process_queue; the trigger endpoint returns 409 when
busy, and the frontend keeps the job queued and retries after 30s.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/api/competitors.py

@@ -297,6 +297,12 @@ async def trigger_manual_scrape(
     if paused_row and paused_row.config_value == 'true':
         raise HTTPException(status_code=400, detail="Scraper is currently paused. Use /unpause first or wait for cooldown.")
 
+    # Only one scrape at a time — concurrent Chromium runs cause the page
+    # timeouts that produce partial results
+    from services.booking_scraper import SCRAPE_LOCK
+    if SCRAPE_LOCK.locked():
+        raise HTTPException(status_code=409, detail="A scrape is already running. Try again when it finishes.")
+
     # Start background task
     background_tasks.add_task(run_scrape_sync, from_date, to_date)
 

backend/services/booking_scraper.py

@@ -12,6 +12,7 @@ Features:
 """
 
 import logging
+import threading
 import uuid
 from datetime import date, datetime, timedelta
 from decimal import Decimal
@@ -24,6 +25,11 @@ from .scraper_backends import ScraperBackend, PlaywrightLocalBackend, HotelData,
 
 logger = logging.getLogger(__name__)
 
+# One scrape at a time, process-wide: concurrent Chromium runs starve each
+# other of memory (page timeouts → partial results) and double the request
+# rate at Booking.com. Guards both manual scrapes and queue processing.
+SCRAPE_LOCK = threading.Lock()
+
 
 def get_scraper_backend(db: Session) -> ScraperBackend:
     """
@@ -445,6 +451,24 @@ async def run_manual_scrape(
     if to_date is None:
         to_date = from_date
 
+    if not SCRAPE_LOCK.acquire(blocking=False):
+        logger.warning(f"Manual scrape {from_date}..{to_date} refused — another scrape is running")
+        return {
+            'success': False,
+            'already_running': True,
+            'error': 'Another scrape is already running. Try again when it finishes.',
+        }
+    try:
+        return await _run_manual_scrape_locked(db, from_date, to_date)
+    finally:
+        SCRAPE_LOCK.release()
+
+
+async def _run_manual_scrape_locked(
+    db: Session,
+    from_date: date,
+    to_date: date
+) -> Dict[str, Any]:
     # Check if paused
     if await is_scraper_paused(db):
         return {
@@ -655,6 +679,20 @@ async def process_queue(db: Session) -> Dict[str, Any]:
     Returns:
         Dict with processing results
     """
+    if not SCRAPE_LOCK.acquire(blocking=False):
+        logger.warning("Queue processing skipped — another scrape is running")
+        return {
+            'success': False,
+            'already_running': True,
+            'error': 'Another scrape is already running.',
+        }
+    try:
+        return await _process_queue_locked(db)
+    finally:
+        SCRAPE_LOCK.release()
+
+
+async def _process_queue_locked(db: Session) -> Dict[str, Any]:
     # Check if paused
     if await is_scraper_paused(db):
         return {

frontend/src/pages/MarketView.tsx

@@ -949,6 +949,8 @@ const RateMatrixTab: React.FC = () => {
   // batch finishes, refetch the matrix, then start the next job.
   const [scrapeQueue, setScrapeQueue] = useState<ScrapeJob[]>([])
   const [scrapeWatch, setScrapeWatch] = useState<{ prevBatch: string | null, startedAt: number, timeoutMs: number } | null>(null)
+  const [dispatchHoldUntil, setDispatchHoldUntil] = useState(0)
+  const [retryTick, setRetryTick] = useState(0)
 
   const enqueueScrape = (from: string, to: string) => {
     setScrapeQueue(q => q.some(j => j.from === from && j.to === to) ? q : [...q, { from, to }])
@@ -969,18 +971,25 @@ const RateMatrixTab: React.FC = () => {
       })
       return (await api.post('/competitors/scrape', { from_date: job.from, to_date: job.to })).data
     },
-    onError: () => {
+    onError: (err: any) => {
       setScrapeWatch(null)
-      setScrapeQueue(q => q.slice(1))
+      if (err?.response?.status === 409) {
+        // Server is busy with another scrape — keep the job queued, retry in 30s
+        setDispatchHoldUntil(Date.now() + 30000)
+        setTimeout(() => setRetryTick(t => t + 1), 31000)
+      } else {
+        setScrapeQueue(q => q.slice(1))
+      }
     },
   })
 
   // Dispatch the next queued job when idle
   useEffect(() => {
+    if (Date.now() < dispatchHoldUntil) return
     if (scrapeQueue.length && !scrapeWatch && !dateScrapeM.isPending) {
       dateScrapeM.mutate(scrapeQueue[0])
     }
-  }, [scrapeQueue, scrapeWatch, dateScrapeM.isPending]) // eslint-disable-line react-hooks/exhaustive-deps
+  }, [scrapeQueue, scrapeWatch, dateScrapeM.isPending, dispatchHoldUntil, retryTick]) // eslint-disable-line react-hooks/exhaustive-deps
 
   // Also serves the date-header Booking.com links via location_name
   const { data: watchStatus } = useQuery<ScraperStatus>({