Reduce queries for waitinglist autoassign n+1 (PRETIXEU-BJJ) (#5819)

* baseline of 574 queries

* reuse event from wle for locked_wle

reduces amount of queries to 556

* keep event accross refresh from db

drops queries from 556 to 471, halving the amount of queries for direct fetches for the event

* make numbers of queries reproducible by prewarming ContentTypeCache

* fix oversight

* correct number of queries to 335

* remove debug tooling

* remove assert_num_queries

src/pretix/base/models/waitinglist.py

@@ -159,6 +159,7 @@ class WaitingListEntry(LoggedModel):
         if availability[1] is None or availability[1] < 1:
             raise WaitingListException(_('This product is currently not available.'))
 
+        event = self.event
         ev = self.subevent or self.event
         if ev.seat_category_mappings.filter(product=self.item).exists():
             # Generally, we advertise the waiting list to be based on quotas only. This makes it dangerous
@@ -191,6 +192,7 @@ class WaitingListEntry(LoggedModel):
 
         with transaction.atomic():
             locked_wle = WaitingListEntry.objects.select_for_update(of=OF_SELF).get(pk=self.pk)
+            locked_wle.event = event
             if locked_wle.voucher:
                 raise WaitingListException(_('A voucher has already been sent to this person.'))
             e = locked_wle.email
@@ -227,6 +229,7 @@ class WaitingListEntry(LoggedModel):
             locked_wle.save()
 
         self.refresh_from_db()
+        self.event = event
 
         with language(self.locale, self.event.settings.region):
             self.send_mail(