Implement deferred join for pagination

judge/utils/deferred_paginator.py

@@ -0,0 +1,65 @@
+from django.core.exceptions import EmptyResultSet
+from django.views.generic import ListView
+
+from judge.utils.raw_sql import join_sql_subquery
+
+
+class DeferredPaginationListView(ListView):
+    paginated_model = None
+
+    def deferred_paginate(self, queryset):
+        return queryset
+
+    def get_context_data(self, *, object_list=None, **kwargs):
+        """Get the context for this view."""
+        queryset = object_list if object_list is not None else self.object_list
+        page_size = self.get_paginate_by(queryset)
+        context_object_name = self.get_context_object_name(queryset)
+        if page_size:
+            queryset_pks = queryset.values_list('pk', flat=True)
+            paginator, page, queryset_pks, is_paginated = self.paginate_queryset(
+                queryset_pks, page_size
+            )
+
+            try:
+                query, params = queryset_pks.query.sql_with_params()
+                queryset = self.__class__.paginated_model.objects.all()
+                join_sql_subquery(
+                    queryset,
+                    subquery=query,
+                    params=list(params),
+                    join_fields=[('id', 'id')],
+                    alias='deferred_object',
+                    related_model=self.__class__.paginated_model,
+                )
+                queryset = self.deferred_paginate(queryset)
+                ordering = self.get_ordering()
+                if ordering:
+                    if isinstance(ordering, str):
+                        ordering = (ordering,)
+                    queryset = queryset.order_by(*ordering)
+            except EmptyResultSet:
+                queryset = []
+
+            page.object_list = queryset
+            context = {
+                "paginator": paginator,
+                "page_obj": page,
+                "is_paginated": is_paginated,
+                "object_list": queryset,
+            }
+        else:
+            context = {
+                "paginator": None,
+                "page_obj": None,
+                "is_paginated": False,
+                "object_list": queryset,
+            }
+        if context_object_name is not None:
+            context[context_object_name] = queryset
+        context.update(kwargs)
+
+        context.setdefault("view", self)
+        if self.extra_context is not None:
+            context.update(self.extra_context)
+        return context

judge/utils/infinite_paginator.py

@@ -20,7 +20,7 @@ class InfinitePage(collections.abc.Sequence):
     This eliminates the need to count the next pages items.
     """
     def __init__(self, object_list, number, unfiltered_queryset, page_size, pad_pages, paginator):
-        self.object_list = list(object_list)
+        self.object_list = object_list
         self.number = number
         self.unfiltered_queryset = unfiltered_queryset
         self.page_size = page_size

judge/views/ranked_submission.py

@@ -63,6 +63,12 @@ def get_queryset(self):
         else:
             return queryset.order_by('-points', 'time')
 
+    def get_ordering(self):
+        if self.is_contest_scoped:
+            return ('-contest__points', 'time')
+        else:
+            return ('-points', 'time')
+
     def get_title(self):
         return _('Best solutions for %s') % self.problem_name
 

judge/views/submission.py

@@ -26,6 +26,7 @@
 from judge.highlight_code import highlight_code
 from judge.models import Contest, Language, Organization, Problem, ProblemTranslation, Profile, Submission
 from judge.models.problem import ProblemTestcaseResultAccess, SubmissionSourceAccess
+from judge.utils.deferred_paginator import DeferredPaginationListView
 from judge.utils.infinite_paginator import InfinitePaginationMixin
 from judge.utils.lazy import memo_lazy
 from judge.utils.problem_data import get_problem_testcases_data
@@ -344,7 +345,7 @@ def filter_submissions_by_visible_problems(queryset, user):
     )
 
 
-class SubmissionsListBase(DiggPaginatorMixin, TitleMixin, ListView):
+class SubmissionsListBase(DiggPaginatorMixin, TitleMixin, DeferredPaginationListView):
     model = Submission
     paginate_by = 50
     show_problem = True
@@ -354,6 +355,8 @@ class SubmissionsListBase(DiggPaginatorMixin, TitleMixin, ListView):
     template_name = 'submission/list.html'
     context_object_name = 'submissions'
     first_page_href = None
+    paginated_model = Submission
+    ordering = '-id'
 
     def get_result_data(self):
         result = self._get_result_data()
@@ -382,6 +385,10 @@ def is_contest_scoped(self):
     def contest(self):
         return self.request.profile.current_contest.contest
 
+    def deferred_paginate(self, queryset):
+        return (queryset.select_related('user__user', 'user__display_badge', 'problem', 'language')
+                        .prefetch_related('contest_object__authors', 'contest_object__curators'))
+
     def _get_queryset(self):
         queryset = Submission.objects.all()
         use_straight_join(queryset)