Waiting list: Fix pathological performance on large series with seating (#4169)

src/pretix/base/services/waitinglist.py

@@ -20,6 +20,7 @@
 # <https://www.gnu.org/licenses/>.
 #
 import sys
+from collections import defaultdict
 from datetime import timedelta
 
 from django.db import transaction
@@ -49,19 +50,28 @@ def assign_automatically(event: Event, user_id: int=None, subevent_id: int=None)
 
     quota_cache = {}
     gone = set()
-    seats_available = {}
+    _seats_available_cache = {}
+    seats_used = defaultdict(int)
 
-    for m in SeatCategoryMapping.objects.filter(event=event).select_related('subevent'):
+    seated_product_set = set(
+        SeatCategoryMapping.objects.filter(event=event).values_list('product_id', 'subevent_id')
+    )
+
+    def _seats_available(item, subevent):
         # See comment in WaitingListEntry.send_voucher() for rationale
-        num_free_seets_for_product = (m.subevent or event).free_seats().filter(product_id=m.product_id).count()
+        subevent_id = subevent.pk if subevent else None
-        num_valid_vouchers_for_product = event.vouchers.filter(
+        if (item.pk, subevent_id) not in _seats_available_cache:
-            Q(valid_until__isnull=True) | Q(valid_until__gte=now()),
+            num_free_seats_for_product = (subevent or event).free_seats().filter(product_id=item.pk).count()
-            block_quota=True,
+            num_valid_vouchers_for_product = event.vouchers.filter(
-            item_id=m.product_id,
+                Q(valid_until__isnull=True) | Q(valid_until__gte=now()),
-            subevent_id=m.subevent_id,
+                block_quota=True,
-            waitinglistentries__isnull=False
+                item_id=item.pk,
-        ).aggregate(free=Sum(F('max_usages') - F('redeemed')))['free'] or 0
+                subevent_id=subevent_id,
-        seats_available[(m.product_id, m.subevent_id)] = num_free_seets_for_product - num_valid_vouchers_for_product
+                waitinglistentries__isnull=False
+            ).aggregate(free=Sum(F('max_usages') - F('redeemed')))['free'] or 0
+            _seats_available_cache[item.pk, subevent_id] = num_free_seats_for_product - num_valid_vouchers_for_product
+
+        return _seats_available_cache[item.pk, subevent_id] - seats_used[item.pk, subevent_id]
 
     prefetch_related_objects(
         [event.organizer],
@@ -103,7 +113,7 @@ def assign_automatically(event: Event, user_id: int=None, subevent_id: int=None)
 
         lock_objects(quotas, shared_lock_objects=[event])
         for wle in qs:
-            if (wle.item, wle.variation, wle.subevent) in gone:
+            if (wle.item_id, wle.variation_id, wle.subevent_id) in gone:
                 continue
             ev = (wle.subevent or event)
             if not ev.presale_is_running or (wle.subevent and not wle.subevent.active):
@@ -111,15 +121,15 @@ def assign_automatically(event: Event, user_id: int=None, subevent_id: int=None)
             if wle.subevent and not wle.subevent.presale_is_running:
                 continue
             if event.settings.waiting_list_auto_disable and event.settings.waiting_list_auto_disable.datetime(wle.subevent or event) <= now():
-                gone.add((wle.item, wle.variation, wle.subevent))
+                gone.add((wle.item_id, wle.variation_id, wle.subevent_id))
                 continue
             if not wle.item.is_available():
-                gone.add((wle.item, wle.variation, wle.subevent))
+                gone.add((wle.item_id, wle.variation_id, wle.subevent_id))
                 continue
 
-            if (wle.item_id, wle.subevent_id) in seats_available:
+            if (wle.item_id, wle.subevent_id) in seated_product_set:
-                if seats_available[wle.item_id, wle.subevent_id] < 1:
+                if _seats_available(wle.item, wle.subevent) < 1:
-                    gone.add((wle.item, wle.variation, wle.subevent))
+                    gone.add((wle.item_id, wle.variation_id, wle.subevent_id))
                     continue
 
             availability = (
@@ -141,10 +151,10 @@ def assign_automatically(event: Event, user_id: int=None, subevent_id: int=None)
                         quota_cache[q.pk][1] - 1 if quota_cache[q.pk][1] is not None else sys.maxsize
                     )
 
-                if (wle.item_id, wle.subevent_id) in seats_available:
+                if (wle.item_id, wle.subevent_id) in seated_product_set:
-                    seats_available[wle.item_id, wle.subevent_id] -= 1
+                    seats_used[wle.item_id, wle.subevent_id] += 1
             else:
-                gone.add((wle.item, wle.variation, wle.subevent))
+                gone.add((wle.item_id, wle.variation_id, wle.subevent_id))
 
     return sent
 

src/tests/base/test_waitinglist.py

@@ -194,6 +194,26 @@ class WaitingListTestCase(TestCase):
             assert WaitingListEntry.objects.filter(voucher__isnull=True).count() == 10
             assert Voucher.objects.count() == 10
 
+    def test_send_auto_no_seat(self):
+        with scope(organizer=self.o):
+            self.quota.items.add(self.item1)
+            self.quota.size = 10
+            self.quota.save()
+            self.event.seat_category_mappings.create(
+                layout_category='Stalls', product=self.item1
+            )
+            self.event.seats.create(seat_number="Foo", product=self.item1, seat_guid="Foo", blocked=True)
+            self.event.seats.create(seat_number="Bar", product=self.item1, seat_guid="Bar", blocked=True)
+            self.event.seats.create(seat_number="Baz", product=self.item1, seat_guid="Baz", blocked=True)
+            WaitingListEntry.objects.create(
+                event=self.event, item=self.item1, email='foo@bar.com'
+            )
+            assign_automatically.apply(args=(self.event.pk,))
+            assert Voucher.objects.count() == 0
+            self.event.seats.create(seat_number="Baz", product=self.item1, seat_guid="Baz", blocked=False)
+            assign_automatically.apply(args=(self.event.pk,))
+            assert Voucher.objects.count() == 1
+
     def test_send_periodic_event_over(self):
         self.event.settings.set('waiting_list_enabled', True)
         self.event.settings.set('waiting_list_auto', True)