Add database cache for quotas

src/pretix/base/services/quotas.py

@@ -0,0 +1,34 @@
+from datetime import timedelta
+
+from django.db import models
+from django.db.models import F, Max, OuterRef, Q, Subquery
+from django.dispatch import receiver
+
+from pretix.base.models import LogEntry, Quota
+from pretix.celery_app import app
+
+from ..signals import periodic_task
+
+
+@receiver(signal=periodic_task)
+def build_all_quota_caches(sender, **kwargs):
+    refresh_quota_cashes.apply_async()
+
+
+@app.task
+def refresh_quota_cashes():
+    last_activity = LogEntry.objects.filter(
+        event=OuterRef('event_id'),
+    ).order_by().values('event').annotate(
+        m=Max('datetime')
+    ).values(
+        'm'
+    )
+    quotas = Quota.objects.annotate(
+        last_activity=Subquery(last_activity, output_field=models.DateTimeField())
+    ).filter(
+        Q(cached_availability_time__isnull=True) |
+        Q(cached_availability_time__lt=F('last_activity') - timedelta(hours=1))
+    )
+    for q in quotas:
+        q.availability()