Bulk-reads and Request caching in Course Grade Report

This reverts commit 5388d5d1.

common/djangoapps/course_modes/models.py

@@ -9,8 +9,11 @@ from config_models.models import ConfigurationModel
 from django.core.exceptions import ValidationError
 from django.db import models
 from django.db.models import Q
+from django.dispatch import receiver
 from django.utils.translation import ugettext_lazy as _
 from openedx.core.djangoapps.xmodule_django.models import CourseKeyField
+from request_cache.middleware import ns_request_cached, RequestCache
+
 
 Mode = namedtuple('Mode',
                   [
@@ -141,6 +144,8 @@ class CourseMode(models.Model):
     DEFAULT_SHOPPINGCART_MODE_SLUG = HONOR
     DEFAULT_SHOPPINGCART_MODE = Mode(HONOR, _('Honor'), 0, '', 'usd', None, None, None, None)
 
+    CACHE_NAMESPACE = u"course_modes.CourseMode.cache."
+
     class Meta(object):
         unique_together = ('course_id', 'mode_slug', 'currency')
 
@@ -265,6 +270,7 @@ class CourseMode(models.Model):
         return [mode.to_tuple() for mode in found_course_modes]
 
     @classmethod
+    @ns_request_cached(CACHE_NAMESPACE)
     def modes_for_course(cls, course_id, include_expired=False, only_selectable=True):
         """
         Returns a list of the non-expired modes for a given course id
@@ -666,6 +672,13 @@ class CourseMode(models.Model):
         )
 
 
+@receiver(models.signals.post_save, sender=CourseMode)
+@receiver(models.signals.post_delete, sender=CourseMode)
+def invalidate_course_mode_cache(sender, **kwargs):   # pylint: disable=unused-argument
+    """Invalidate the cache of course modes. """
+    RequestCache.clear_request_cache(name=CourseMode.CACHE_NAMESPACE)
+
+
 class CourseModesArchive(models.Model):
     """
     Store the past values of course_mode that a course had in the past. We decided on having

common/djangoapps/course_modes/tests/test_models.py

@@ -16,7 +16,7 @@ from opaque_keys.edx.locator import CourseLocator
 import pytz
 
 from course_modes.helpers import enrollment_mode_display
-from course_modes.models import CourseMode, Mode
+from course_modes.models import CourseMode, Mode, invalidate_course_mode_cache
 from course_modes.tests.factories import CourseModeFactory
 
 
@@ -31,6 +31,9 @@ class CourseModeModelTest(TestCase):
         self.course_key = SlashSeparatedCourseKey('Test', 'TestCourse', 'TestCourseRun')
         CourseMode.objects.all().delete()
 
+    def tearDown(self):
+        invalidate_course_mode_cache(sender=None)
+
     def create_mode(
             self,
             mode_slug,

common/djangoapps/request_cache/__init__.py

@@ -41,6 +41,16 @@ def get_cache(name):
     return middleware.RequestCache.get_request_cache(name)
 
 
+def clear_cache(name):
+    """
+    Clears the request cache named ``name``.
+
+    Arguments:
+        name (str): The name of the request cache to clear
+    """
+    return middleware.RequestCache.clear_request_cache(name)
+
+
 def get_request():
     """
     Return the current request.

common/djangoapps/request_cache/middleware.py

@@ -39,11 +39,14 @@ class RequestCache(object):
         return crum.get_current_request()
 
     @classmethod
-    def clear_request_cache(cls):
+    def clear_request_cache(cls, name=None):
         """
         Empty the request cache.
         """
-        REQUEST_CACHE.data = {}
+        if name is None:
+            REQUEST_CACHE.data = {}
+        elif REQUEST_CACHE.data.get(name):
+            REQUEST_CACHE.data[name] = {}
 
     def process_request(self, request):
         self.clear_request_cache()
@@ -82,25 +85,43 @@ def request_cached(f):
               cache the value it returns, and return that cached value for subsequent calls with the
               same args/kwargs within a single request
     """
-    def wrapper(*args, **kwargs):
-        """
-        Wrapper function to decorate with.
-        """
-        # Check to see if we have a result in cache.  If not, invoke our wrapped
-        # function.  Cache and return the result to the caller.
-        rcache = RequestCache.get_request_cache()
-        cache_key = func_call_cache_key(f, *args, **kwargs)
+    return ns_request_cached()(f)
 
-        if cache_key in rcache.data:
-            return rcache.data.get(cache_key)
-        else:
-            result = f(*args, **kwargs)
-            rcache.data[cache_key] = result
 
-            return result
+def ns_request_cached(namespace=None):
+    """
+    Same as request_cached above, except an optional namespace can be passed in to compartmentalize the cache.
+
+    Arguments:
+        namespace (string): An optional namespace to use for the cache.  Useful if the caller wants to manage
+            their own sub-cache by, for example, calling RequestCache.clear_request_cache for their own namespace.
+    """
+    def outer_wrapper(f):
+        """
+        Outer wrapper that decorates the given function
 
-    wrapper.request_cached_contained_func = f
-    return wrapper
+        Arguments:
+            f (func): the function to wrap
+        """
+        def inner_wrapper(*args, **kwargs):
+            """
+            Wrapper function to decorate with.
+            """
+            # Check to see if we have a result in cache.  If not, invoke our wrapped
+            # function.  Cache and return the result to the caller.
+            rcache = RequestCache.get_request_cache(namespace)
+            rcache = rcache.data if namespace is None else rcache
+            cache_key = func_call_cache_key(f, *args, **kwargs)
+
+            if cache_key in rcache:
+                return rcache.get(cache_key)
+            else:
+                result = f(*args, **kwargs)
+                rcache[cache_key] = result
+                return result
+
+        return inner_wrapper
+    return outer_wrapper
 
 
 def func_call_cache_key(func, *args, **kwargs):

common/djangoapps/student/models.py

@@ -998,7 +998,9 @@ class CourseEnrollment(models.Model):
     history = HistoricalRecords()
 
     # cache key format e.g enrollment.<username>.<course_key>.mode = 'honor'
-    COURSE_ENROLLMENT_CACHE_KEY = u"enrollment.{}.{}.mode"
+    COURSE_ENROLLMENT_CACHE_KEY = u"enrollment.{}.{}.mode"  # TODO Can this be removed?  It doesn't seem to be used.
+
+    MODE_CACHE_NAMESPACE = u'CourseEnrollment.mode_and_active'
 
     class Meta(object):
         unique_together = (('user', 'course_id'),)
@@ -1698,11 +1700,27 @@ class CourseEnrollment(models.Model):
         return enrollment_state
 
     @classmethod
+    def bulk_fetch_enrollment_states(cls, users, course_key):
+        """
+        Bulk pre-fetches the enrollment states for the given users
+        for the given course.
+        """
+        # before populating the cache with another bulk set of data,
+        # remove previously cached entries to keep memory usage low.
+        request_cache.clear_cache(cls.MODE_CACHE_NAMESPACE)
+
+        records = cls.objects.filter(user__in=users, course_id=course_key).select_related('user__id')
+        cache = cls._get_mode_active_request_cache()
+        for record in records:
+            enrollment_state = CourseEnrollmentState(record.mode, record.is_active)
+            cls._update_enrollment(cache, record.user.id, course_key, enrollment_state)
+
+    @classmethod
     def _get_mode_active_request_cache(cls):
         """
         Returns the request-specific cache for CourseEnrollment
         """
-        return request_cache.get_cache('CourseEnrollment.mode_and_active')
+        return request_cache.get_cache(cls.MODE_CACHE_NAMESPACE)
 
     @classmethod
     def _get_enrollment_in_request_cache(cls, user, course_key):
@@ -1718,7 +1736,15 @@ class CourseEnrollment(models.Model):
         Updates the cached value for the user's enrollment in the
         request cache.
         """
-        cls._get_mode_active_request_cache()[(user.id, course_key)] = enrollment_state
+        cls._update_enrollment(cls._get_mode_active_request_cache(), user.id, course_key, enrollment_state)
+
+    @classmethod
+    def _update_enrollment(cls, cache, user_id, course_key, enrollment_state):
+        """
+        Updates the cached value for the user's enrollment in the
+        given cache.
+        """
+        cache[(user_id, course_key)] = enrollment_state
 
 
 @receiver(models.signals.post_save, sender=CourseEnrollment)

common/djangoapps/student/roles.py

@@ -4,10 +4,12 @@ adding users, removing users, and listing members
 """
 
 from abc import ABCMeta, abstractmethod
+from collections import defaultdict
 
 from django.contrib.auth.models import User
 import logging
 
+from request_cache import get_cache
 from student.models import CourseAccessRole
 from openedx.core.djangoapps.xmodule_django.models import CourseKeyField
 
@@ -34,14 +36,38 @@ def register_access_role(cls):
     return cls
 
 
+class BulkRoleCache(object):
+    CACHE_NAMESPACE = u"student.roles.BulkRoleCache"
+    CACHE_KEY = u'roles_by_user'
+
+    @classmethod
+    def prefetch(cls, users):
+        roles_by_user = defaultdict(set)
+        get_cache(cls.CACHE_NAMESPACE)[cls.CACHE_KEY] = roles_by_user
+
+        for role in CourseAccessRole.objects.filter(user__in=users).select_related('user__id'):
+            roles_by_user[role.user.id].add(role)
+
+        users_without_roles = filter(lambda u: u.id not in roles_by_user, users)
+        for user in users_without_roles:
+            roles_by_user[user.id] = set()
+
+    @classmethod
+    def get_user_roles(cls, user):
+        return get_cache(cls.CACHE_NAMESPACE)[cls.CACHE_KEY][user.id]
+
+
 class RoleCache(object):
     """
     A cache of the CourseAccessRoles held by a particular user
     """
     def __init__(self, user):
-        self._roles = set(
-            CourseAccessRole.objects.filter(user=user).all()
-        )
+        try:
+            self._roles = BulkRoleCache.get_user_roles(user)
+        except KeyError:
+            self._roles = set(
+                CourseAccessRole.objects.filter(user=user).all()
+            )
 
     def has_role(self, role, course_id, org):
         """

lms/djangoapps/certificates/models.py

@@ -493,6 +493,18 @@ def handle_course_cert_awarded(sender, user, course_key, **kwargs):  # pylint: d
 
 
 def certificate_status_for_student(student, course_id):
+    """
+    This returns a dictionary with a key for status, and other information.
+    See certificate_status for more information.
+    """
+    try:
+        generated_certificate = GeneratedCertificate.objects.get(user=student, course_id=course_id)
+    except GeneratedCertificate.DoesNotExist:
+        generated_certificate = None
+    return certificate_status(generated_certificate)
+
+
+def certificate_status(generated_certificate):
     '''
     This returns a dictionary with a key for status, and other information.
     The status is one of the following:
@@ -527,9 +539,7 @@ def certificate_status_for_student(student, course_id):
     # the course_modes app is loaded, resulting in a Django deprecation warning.
     from course_modes.models import CourseMode
 
-    try:
-        generated_certificate = GeneratedCertificate.objects.get(  # pylint: disable=no-member
-            user=student, course_id=course_id)
+    if generated_certificate:
         cert_status = {
             'status': generated_certificate.status,
             'mode': generated_certificate.mode,
@@ -539,7 +549,7 @@ def certificate_status_for_student(student, course_id):
             cert_status['grade'] = generated_certificate.grade
 
         if generated_certificate.mode == 'audit':
-            course_mode_slugs = [mode.slug for mode in CourseMode.modes_for_course(course_id)]
+            course_mode_slugs = [mode.slug for mode in CourseMode.modes_for_course(generated_certificate.course_id)]
             # Short term fix to make sure old audit users with certs still see their certs
             # only do this if there if no honor mode
             if 'honor' not in course_mode_slugs:
@@ -550,31 +560,24 @@ def certificate_status_for_student(student, course_id):
             cert_status['download_url'] = generated_certificate.download_url
 
         return cert_status
-
-    except GeneratedCertificate.DoesNotExist:
-        pass
-    return {'status': CertificateStatuses.unavailable, 'mode': GeneratedCertificate.MODES.honor, 'uuid': None}
+    else:
+        return {'status': CertificateStatuses.unavailable, 'mode': GeneratedCertificate.MODES.honor, 'uuid': None}
 
 
-def certificate_info_for_user(user, course_id, grade, user_is_whitelisted=None):
+def certificate_info_for_user(user, grade, user_is_whitelisted, user_certificate):
     """
     Returns the certificate info for a user for grade report.
     """
-    if user_is_whitelisted is None:
-        user_is_whitelisted = CertificateWhitelist.objects.filter(
-            user=user, course_id=course_id, whitelist=True
-        ).exists()
-
     certificate_is_delivered = 'N'
     certificate_type = 'N/A'
     eligible_for_certificate = 'Y' if (user_is_whitelisted or grade is not None) and user.profile.allow_certificate \
         else 'N'
 
-    certificate_status = certificate_status_for_student(user, course_id)
-    certificate_generated = certificate_status['status'] == CertificateStatuses.downloadable
+    status = certificate_status(user_certificate)
+    certificate_generated = status['status'] == CertificateStatuses.downloadable
     if certificate_generated:
         certificate_is_delivered = 'Y'
-        certificate_type = certificate_status['mode']
+        certificate_type = status['mode']
 
     return [eligible_for_certificate, certificate_is_delivered, certificate_type]
 

lms/djangoapps/certificates/tests/tests.py

@@ -54,11 +54,11 @@ class CertificatesModelTest(ModuleStoreTestCase, MilestonesTestCaseMixin):
         Verify that certificate_info_for_user works.
         """
         student = UserFactory()
-        course = CourseFactory.create(org='edx', number='verified', display_name='Verified Course')
+        _ = CourseFactory.create(org='edx', number='verified', display_name='Verified Course')
         student.profile.allow_certificate = allow_certificate
         student.profile.save()
 
-        certificate_info = certificate_info_for_user(student, course.id, grade, whitelisted)
+        certificate_info = certificate_info_for_user(student, grade, whitelisted, user_certificate=None)
         self.assertEqual(certificate_info, output)
 
     @unpack
@@ -81,14 +81,13 @@ class CertificatesModelTest(ModuleStoreTestCase, MilestonesTestCaseMixin):
         student.profile.allow_certificate = allow_certificate
         student.profile.save()
 
-        GeneratedCertificateFactory.create(
+        certificate = GeneratedCertificateFactory.create(
             user=student,
             course_id=course.id,
             status=CertificateStatuses.downloadable,
             mode='honor'
         )
-
-        certificate_info = certificate_info_for_user(student, course.id, grade, whitelisted)
+        certificate_info = certificate_info_for_user(student, grade, whitelisted, certificate)
         self.assertEqual(certificate_info, output)
 
     def test_course_ids_with_certs_for_user(self):

lms/djangoapps/grades/models.py

@@ -25,6 +25,7 @@ from track.event_transaction_utils import get_event_transaction_id, get_event_tr
 from coursewarehistoryextended.fields import UnsignedBigIntAutoField
 from opaque_keys.edx.keys import CourseKey, UsageKey
 from openedx.core.djangoapps.xmodule_django.models import CourseKeyField, UsageKeyField
+from request_cache import get_cache
 
 from .config import waffle
 
@@ -522,6 +523,8 @@ class PersistentCourseGrade(DeleteGradesMixin, TimeStampedModel):
     # Information related to course completion
     passed_timestamp = models.DateTimeField(u'Date learner earned a passing grade', blank=True, null=True)
 
+    CACHE_NAMESPACE = u"grades.models.PersistentCourseGrade"
+
     def __unicode__(self):
         """
         Returns a string representation of this model.
@@ -536,6 +539,21 @@ class PersistentCourseGrade(DeleteGradesMixin, TimeStampedModel):
         ])
 
     @classmethod
+    def _cache_key(cls, course_id):
+        return u"grades_cache.{}".format(course_id)
+
+    @classmethod
+    def prefetch(cls, course_id, users):
+        """
+        Prefetches grades for the given users for the given course.
+        """
+        get_cache(cls.CACHE_NAMESPACE)[cls._cache_key(course_id)] = {
+            grade.user_id: grade
+            for grade in
+            cls.objects.filter(user_id__in=[user.id for user in users], course_id=course_id)
+        }
+
+    @classmethod
     def read(cls, user_id, course_id):
         """
         Reads a grade from database
@@ -546,7 +564,17 @@ class PersistentCourseGrade(DeleteGradesMixin, TimeStampedModel):
 
         Raises PersistentCourseGrade.DoesNotExist if applicable
         """
-        return cls.objects.get(user_id=user_id, course_id=course_id)
+        try:
+            prefetched_grades = get_cache(cls.CACHE_NAMESPACE)[cls._cache_key(course_id)]
+            try:
+                return prefetched_grades[user_id]
+            except KeyError:
+                # user's grade is not in the prefetched list, so
+                # assume they have no grade
+                raise cls.DoesNotExist
+        except KeyError:
+            # grades were not prefetched for the course, so fetch it
+            return cls.objects.get(user_id=user_id, course_id=course_id)
 
     @classmethod
     def update_or_create(cls, user_id, course_id, **kwargs):

lms/djangoapps/grades/new/course_grade_factory.py

@@ -81,7 +81,6 @@ class CourseGradeFactory(object):
             users,
             course=None,
             collected_block_structure=None,
-            course_structure=None,
             course_key=None,
             force_update=False,
     ):
@@ -99,7 +98,9 @@ class CourseGradeFactory(object):
         #    compute the grade for all students.
         # 2. Optimization: the collected course_structure is not
         #    retrieved from the data store multiple times.
-        course_data = CourseData(None, course, collected_block_structure, course_structure, course_key)
+        course_data = CourseData(
+            user=None, course=course, collected_block_structure=collected_block_structure, course_key=course_key,
+        )
         for user in users:
             with dog_stats_api.timer(
                     'lms.grades.CourseGradeFactory.iter',
@@ -107,7 +108,9 @@ class CourseGradeFactory(object):
             ):
                 try:
                     method = CourseGradeFactory().update if force_update else CourseGradeFactory().create
-                    course_grade = method(user, course, course_data.collected_structure, course_structure, course_key)
+                    course_grade = method(
+                        user, course_data.course, course_data.collected_structure, course_key=course_key,
+                    )
                     yield self.GradeResult(user, course_grade, None)
 
                 except Exception as exc:  # pylint: disable=broad-except

lms/djangoapps/grades/tests/test_new.py

@@ -178,10 +178,10 @@ class TestCourseGradeFactory(GradeTestBase):
             self.assertEqual(course_grade.letter_grade, u'Pass' if expected_pass else None)
             self.assertEqual(course_grade.percent, 0.5)
 
-        with self.assertNumQueries(12), mock_get_score(1, 2):
+        with self.assertNumQueries(11), mock_get_score(1, 2):
             _assert_create(expected_pass=True)
 
-        with self.assertNumQueries(15), mock_get_score(1, 2):
+        with self.assertNumQueries(13), mock_get_score(1, 2):
             grade_factory.update(self.request.user, self.course)
 
         with self.assertNumQueries(1):
@@ -189,7 +189,7 @@ class TestCourseGradeFactory(GradeTestBase):
 
         self._update_grading_policy(passing=0.9)
 
-        with self.assertNumQueries(8):
+        with self.assertNumQueries(6):
             _assert_create(expected_pass=False)
 
     @ddt.data(True, False)

lms/djangoapps/grades/tests/test_tasks.py

@@ -409,8 +409,8 @@ class ComputeGradesForCourseTest(HasCourseWithProblemsMixin, ModuleStoreTestCase
 
     @ddt.data(*xrange(1, 12, 3))
     def test_database_calls(self, batch_size):
-        per_user_queries = 17 * min(batch_size, 6)  # No more than 6 due to offset
-        with self.assertNumQueries(5 + per_user_queries):
+        per_user_queries = 15 * min(batch_size, 6)  # No more than 6 due to offset
+        with self.assertNumQueries(6 + per_user_queries):
             with check_mongo_calls(1):
                 compute_grades_for_course_v2.delay(
                     course_key=six.text_type(self.course.id),

lms/djangoapps/instructor_task/tests/test_tasks_helper.py

@@ -34,9 +34,11 @@ from lms.djangoapps.teams.tests.factories import CourseTeamFactory, CourseTeamMe
 from lms.djangoapps.verify_student.tests.factories import SoftwareSecurePhotoVerificationFactory
 from openedx.core.djangoapps.course_groups.models import CourseUserGroupPartitionGroup, CohortMembership
 from openedx.core.djangoapps.course_groups.tests.helpers import CohortFactory
+from openedx.core.djangoapps.credit.tests.factories import CreditCourseFactory
 import openedx.core.djangoapps.user_api.course_tag.api as course_tag_api
 from openedx.core.djangoapps.user_api.partition_schemes import RandomUserPartitionScheme
 from openedx.core.djangoapps.util.testing import ContentGroupTestCase, TestConditionalContent
+from request_cache.middleware import RequestCache
 from shoppingcart.models import (
     Order, PaidCourseRegistration, CourseRegistrationCode, Invoice,
     CourseRegistrationCodeInvoiceItem, InvoiceTransaction, Coupon
@@ -44,8 +46,9 @@ from shoppingcart.models import (
 from student.models import CourseEnrollment, CourseEnrollmentAllowed, ManualEnrollmentAudit, ALLOWEDTOENROLL_TO_ENROLLED
 from student.tests.factories import CourseEnrollmentFactory, CourseModeFactory, UserFactory
 from survey.models import SurveyForm, SurveyAnswer
+from xmodule.modulestore import ModuleStoreEnum
 from xmodule.modulestore.tests.django_utils import SharedModuleStoreTestCase
-from xmodule.modulestore.tests.factories import CourseFactory, ItemFactory
+from xmodule.modulestore.tests.factories import CourseFactory, ItemFactory, check_mongo_calls
 from xmodule.partitions.partitions import Group, UserPartition
 
 from ..models import ReportStore
@@ -321,6 +324,44 @@ class TestInstructorGradeReport(InstructorGradeReportTestCase):
         result = CourseGradeReport.generate(None, None, self.course.id, None, 'graded')
         self.assertDictContainsSubset({'attempted': 1, 'succeeded': 1, 'failed': 0}, result)
 
+    @ddt.data(
+        (ModuleStoreEnum.Type.mongo, 4),
+        (ModuleStoreEnum.Type.split, 3),
+    )
+    @ddt.unpack
+    def test_query_counts(self, store_type, mongo_count):
+        with self.store.default_store(store_type):
+            experiment_group_a = Group(2, u'Expériment Group A')
+            experiment_group_b = Group(3, u'Expériment Group B')
+            experiment_partition = UserPartition(
+                1,
+                u'Content Expériment Configuration',
+                u'Group Configuration for Content Expériments',
+                [experiment_group_a, experiment_group_b],
+                scheme_id='random'
+            )
+            course = CourseFactory.create(
+                cohort_config={'cohorted': True, 'auto_cohort': True, 'auto_cohort_groups': ['cohort 1', 'cohort 2']},
+                user_partitions=[experiment_partition],
+                teams_configuration={
+                    'max_size': 2, 'topics': [{'topic-id': 'topic', 'name': 'Topic', 'description': 'A Topic'}]
+                },
+            )
+        _ = CreditCourseFactory(course_key=course.id)
+
+        num_users = 5
+        for _ in range(num_users):
+            user = UserFactory.create()
+            CourseEnrollment.enroll(user, course.id, mode='verified')
+            SoftwareSecurePhotoVerificationFactory.create(user=user, status='approved')
+
+        RequestCache.clear_request_cache()
+
+        with patch('lms.djangoapps.instructor_task.tasks_helper.runner._get_current_task'):
+            with check_mongo_calls(mongo_count):
+                with self.assertNumQueries(41):
+                    CourseGradeReport.generate(None, None, course.id, None, 'graded')
+
 
 class TestTeamGradeReport(InstructorGradeReportTestCase):
     """ Test that teams appear correctly in the grade report when it is enabled for the course. """
@@ -1783,7 +1824,7 @@ class TestCertificateGeneration(InstructorTaskModuleTestCase):
             'failed': 3,
             'skipped': 2
         }
-        with self.assertNumQueries(186):
+        with self.assertNumQueries(171):
             self.assertCertificatesGenerated(task_input, expected_results)
 
         expected_results = {

lms/djangoapps/verify_student/models.py

@@ -210,12 +210,19 @@ class PhotoVerification(StatusModel):
 
         This will check for the user's *initial* verification.
         """
+        return cls.verified_query(earliest_allowed_date).filter(user=user).exists()
+
+    @classmethod
+    def verified_query(cls, earliest_allowed_date=None):
+        """
+        Return a query set for all records with 'approved' state
+        that are still valid according to the earliest_allowed_date
+        value or policy settings.
+        """
         return cls.objects.filter(
-            user=user,
             status="approved",
-            created_at__gte=(earliest_allowed_date
-                             or cls._earliest_allowed_date())
-        ).exists()
+            created_at__gte=(earliest_allowed_date or cls._earliest_allowed_date()),
+        )
 
     @classmethod
     def verification_valid_or_pending(cls, user, earliest_allowed_date=None, queryset=None):
@@ -951,14 +958,15 @@ class SoftwareSecurePhotoVerification(PhotoVerification):
         return response
 
     @classmethod
-    def verification_status_for_user(cls, user, course_id, user_enrollment_mode):
+    def verification_status_for_user(cls, user, course_id, user_enrollment_mode, user_is_verified=None):
         """
         Returns the verification status for use in grade report.
         """
         if user_enrollment_mode not in CourseMode.VERIFIED_MODES:
             return 'N/A'
 
-        user_is_verified = cls.user_is_verified(user)
+        if user_is_verified is None:
+            user_is_verified = cls.user_is_verified(user)
 
         if not user_is_verified:
             return 'Not ID Verified'

openedx/core/djangoapps/course_groups/cohorts.py

@@ -14,7 +14,8 @@ from django.utils.translation import ugettext as _
 
 from courseware import courses
 from eventtracking import tracker
-from request_cache.middleware import RequestCache, request_cached
+import request_cache
+from request_cache.middleware import request_cached
 from student.models import get_user_by_username_or_email
 
 from .models import (
@@ -146,8 +147,45 @@ def get_cohorted_commentables(course_key):
     return ans
 
 
+COHORT_CACHE_NAMESPACE = u"cohorts.get_cohort"
+
+
+def _cohort_cache_key(user_id, course_key):
+    """
+    Returns the cache key for the given user_id and course_key.
+    """
+    return u"{}.{}".format(user_id, course_key)
+
+
+def bulk_cache_cohorts(course_key, users):
+    """
+    Pre-fetches and caches the cohort assignments for the
+    given users, for later fast retrieval by get_cohort.
+    """
+    # before populating the cache with another bulk set of data,
+    # remove previously cached entries to keep memory usage low.
+    request_cache.clear_cache(COHORT_CACHE_NAMESPACE)
+    cache = request_cache.get_cache(COHORT_CACHE_NAMESPACE)
+
+    if is_course_cohorted(course_key):
+        cohorts_by_user = {
+            membership.user: membership
+            for membership in
+            CohortMembership.objects.filter(user__in=users, course_id=course_key).select_related('user__id')
+        }
+        for user, membership in cohorts_by_user.iteritems():
+            cache[_cohort_cache_key(user.id, course_key)] = membership.course_user_group
+        uncohorted_users = filter(lambda u: u not in cohorts_by_user, users)
+    else:
+        uncohorted_users = users
+
+    for user in uncohorted_users:
+        cache[_cohort_cache_key(user.id, course_key)] = None
+
+
 def get_cohort(user, course_key, assign=True, use_cached=False):
-    """Returns the user's cohort for the specified course.
+    """
+    Returns the user's cohort for the specified course.
 
     The cohort for the user is cached for the duration of a request. Pass
     use_cached=True to use the cached value instead of fetching from the
@@ -166,19 +204,19 @@ def get_cohort(user, course_key, assign=True, use_cached=False):
     Raises:
        ValueError if the CourseKey doesn't exist.
     """
-    request_cache = RequestCache.get_request_cache()
-    cache_key = u"cohorts.get_cohort.{}.{}".format(user.id, course_key)
+    cache = request_cache.get_cache(COHORT_CACHE_NAMESPACE)
+    cache_key = _cohort_cache_key(user.id, course_key)
 
-    if use_cached and cache_key in request_cache.data:
-        return request_cache.data[cache_key]
+    if use_cached and cache_key in cache:
+        return cache[cache_key]
 
-    request_cache.data.pop(cache_key, None)
+    cache.pop(cache_key, None)
 
     # First check whether the course is cohorted (users shouldn't be in a cohort
     # in non-cohorted courses, but settings can change after course starts)
     course_cohort_settings = get_course_cohort_settings(course_key)
     if not course_cohort_settings.is_cohorted:
-        return request_cache.data.setdefault(cache_key, None)
+        return cache.setdefault(cache_key, None)
 
     # If course is cohorted, check if the user already has a cohort.
     try:
@@ -186,7 +224,7 @@ def get_cohort(user, course_key, assign=True, use_cached=False):
             course_id=course_key,
             user_id=user.id,
         )
-        return request_cache.data.setdefault(cache_key, membership.course_user_group)
+        return cache.setdefault(cache_key, membership.course_user_group)
     except CohortMembership.DoesNotExist:
         # Didn't find the group. If we do not want to assign, return here.
         if not assign:
@@ -201,7 +239,7 @@ def get_cohort(user, course_key, assign=True, use_cached=False):
                 user=user,
                 course_user_group=get_random_cohort(course_key)
             )
-            return request_cache.data.setdefault(cache_key, membership.course_user_group)
+            return cache.setdefault(cache_key, membership.course_user_group)
     except IntegrityError as integrity_error:
         # An IntegrityError is raised when multiple workers attempt to
         # create the same row in one of the cohort model entries:
@@ -419,21 +457,21 @@ def get_group_info_for_cohort(cohort, use_cached=False):
     use_cached=True to use the cached value instead of fetching from the
     database.
     """
-    request_cache = RequestCache.get_request_cache()
-    cache_key = u"cohorts.get_group_info_for_cohort.{}".format(cohort.id)
+    cache = request_cache.get_cache(u"cohorts.get_group_info_for_cohort")
+    cache_key = unicode(cohort.id)
 
-    if use_cached and cache_key in request_cache.data:
-        return request_cache.data[cache_key]
+    if use_cached and cache_key in cache:
+        return cache[cache_key]
 
-    request_cache.data.pop(cache_key, None)
+    cache.pop(cache_key, None)
 
     try:
         partition_group = CourseUserGroupPartitionGroup.objects.get(course_user_group=cohort)
-        return request_cache.data.setdefault(cache_key, (partition_group.group_id, partition_group.partition_id))
+        return cache.setdefault(cache_key, (partition_group.group_id, partition_group.partition_id))
     except CourseUserGroupPartitionGroup.DoesNotExist:
         pass
 
-    return request_cache.data.setdefault(cache_key, (None, None))
+    return cache.setdefault(cache_key, (None, None))
 
 
 def set_assignment_type(user_group, assignment_type):

openedx/core/djangoapps/credit/models.py

@@ -22,6 +22,7 @@ from model_utils.models import TimeStampedModel
 import pytz
 from simple_history.models import HistoricalRecords
 from openedx.core.djangoapps.xmodule_django.models import CourseKeyField
+from request_cache.middleware import ns_request_cached, RequestCache
 
 
 CREDIT_PROVIDER_ID_REGEX = r"[a-z,A-Z,0-9,\-]+"
@@ -290,6 +291,8 @@ class CreditRequirement(TimeStampedModel):
     criteria = JSONField()
     active = models.BooleanField(default=True)
 
+    CACHE_NAMESPACE = u"credit.CreditRequirement.cache."
+
     class Meta(object):
         unique_together = ('namespace', 'name', 'course')
         ordering = ["order"]
@@ -331,6 +334,7 @@ class CreditRequirement(TimeStampedModel):
         return credit_requirement, created
 
     @classmethod
+    @ns_request_cached(CACHE_NAMESPACE)
     def get_course_requirements(cls, course_key, namespace=None, name=None):
         """
         Get credit requirements of a given course.
@@ -392,6 +396,13 @@ class CreditRequirement(TimeStampedModel):
             return None
 
 
+@receiver(models.signals.post_save, sender=CreditRequirement)
+@receiver(models.signals.post_delete, sender=CreditRequirement)
+def invalidate_credit_requirement_cache(sender, **kwargs):   # pylint: disable=unused-argument
+    """Invalidate the cache of credit requirements. """
+    RequestCache.clear_request_cache(name=CreditRequirement.CACHE_NAMESPACE)
+
+
 class CreditRequirementStatus(TimeStampedModel):
     """
     This model represents the status of each requirement.

openedx/core/djangoapps/credit/tests/test_api.py

@@ -664,7 +664,7 @@ class CreditRequirementApiTests(CreditApiTestBase):
         self.assertFalse(api.is_user_eligible_for_credit(user.username, self.course_key))
 
         # Satisfy the other requirement
-        with self.assertNumQueries(25):
+        with self.assertNumQueries(24):
             api.set_credit_requirement_status(
                 user,
                 self.course_key,
@@ -718,7 +718,7 @@ class CreditRequirementApiTests(CreditApiTestBase):
         # Delete the eligibility entries and satisfy the user's eligibility
         # requirement again to trigger eligibility notification
         CreditEligibility.objects.all().delete()
-        with self.assertNumQueries(17):
+        with self.assertNumQueries(16):
             api.set_credit_requirement_status(
                 user,
                 self.course_key,

openedx/core/djangoapps/user_api/course_tag/api.py

@@ -7,6 +7,8 @@ Stores global metadata using the UserPreference model, and per-course metadata u
 UserCourseTag model.
 """
 
+from collections import defaultdict
+from request_cache import get_cache
 from ..models import UserCourseTag
 
 # Scopes
@@ -15,6 +17,42 @@ from ..models import UserCourseTag
 COURSE_SCOPE = 'course'
 
 
+class BulkCourseTags(object):
+    CACHE_NAMESPACE = u'user_api.course_tag.api'
+
+    @classmethod
+    def prefetch(cls, course_id, users):
+        """
+        Prefetches the value of the course tags for the specified users
+        for the specified course_id.
+
+        Args:
+            users: iterator of User objects
+            course_id: course identifier (CourseKey)
+
+        Returns:
+            course_tags: a dict of dicts,
+                where the primary key is the user's id
+                and the secondary key is the course tag's key
+        """
+        course_tags = defaultdict(dict)
+        for tag in UserCourseTag.objects.filter(user__in=users, course_id=course_id).select_related('user__id'):
+            course_tags[tag.user.id][tag.key] = tag.value
+        get_cache(cls.CACHE_NAMESPACE)[cls._cache_key(course_id)] = course_tags
+
+    @classmethod
+    def get_course_tag(cls, user_id, course_id, key):
+        return get_cache(cls.CACHE_NAMESPACE)[cls._cache_key(course_id)][user_id][key]
+
+    @classmethod
+    def is_prefetched(cls, course_id):
+        return cls._cache_key(course_id) in get_cache(cls.CACHE_NAMESPACE)
+
+    @classmethod
+    def _cache_key(cls, course_id):
+        return u'course_tag.{}'.format(course_id)
+
+
 def get_course_tag(user, course_id, key):
     """
     Gets the value of the user's course tag for the specified key in the specified
@@ -28,6 +66,11 @@ def get_course_tag(user, course_id, key):
     Returns:
         string value, or None if there is no value saved
     """
+    if BulkCourseTags.is_prefetched(course_id):
+        try:
+            return BulkCourseTags.get_course_tag(user.id, course_id, key)
+        except KeyError:
+            return None
     try:
         record = UserCourseTag.objects.get(
             user=user,

openedx/core/djangoapps/user_api/partition_schemes.py

@@ -70,7 +70,7 @@ class RandomUserPartitionScheme(object):
                     exc_info=True
                 )
 
-        if group is None and assign:
+        if group is None and assign and not course_tag_api.BulkCourseTags.is_prefetched(course_key):
             if not user_partition.groups:
                 raise UserPartitionError('Cannot assign user to an empty user partition')
 

openedx/core/djangoapps/user_api/tests/test_partition_schemes.py

@@ -26,6 +26,11 @@ class MemoryCourseTagAPI(object):
         """Gets the value of ``key``"""
         self._tags[course_id][key] = value
 
+    class BulkCourseTags(object):
+        @classmethod
+        def is_prefetched(self, course_id):
+            return False
+
 
 class TestRandomUserPartitionScheme(PartitionTestCase):
     """

openedx/core/djangoapps/verified_track_content/models.py

@@ -5,17 +5,17 @@ from django.db import models
 from django.utils.translation import ugettext_lazy
 from django.dispatch import receiver
 from django.db.models.signals import post_save, pre_save
+import logging
 
-from openedx.core.djangoapps.xmodule_django.models import CourseKeyField
-from student.models import CourseEnrollment
 from lms.djangoapps.courseware.courses import get_course_by_id
-
+from openedx.core.djangoapps.xmodule_django.models import CourseKeyField
 from openedx.core.djangoapps.verified_track_content.tasks import sync_cohort_with_mode
 from openedx.core.djangoapps.course_groups.cohorts import (
     get_course_cohorts, CourseCohort, is_course_cohorted, get_random_cohort
 )
+from request_cache.middleware import ns_request_cached, RequestCache
+from student.models import CourseEnrollment
 
-import logging
 
 log = logging.getLogger(__name__)
 
@@ -97,6 +97,8 @@ class VerifiedTrackCohortedCourse(models.Model):
 
     enabled = models.BooleanField()
 
+    CACHE_NAMESPACE = u"verified_track_content.VerifiedTrackCohortedCourse.cache."
+
     def __unicode__(self):
         return u"Course: {}, enabled: {}".format(unicode(self.course_key), self.enabled)
 
@@ -119,6 +121,7 @@ class VerifiedTrackCohortedCourse(models.Model):
             return None
 
     @classmethod
+    @ns_request_cached(CACHE_NAMESPACE)
     def is_verified_track_cohort_enabled(cls, course_key):
         """
         Checks whether or not verified track cohort is enabled for the given course.
@@ -134,3 +137,10 @@ class VerifiedTrackCohortedCourse(models.Model):
             return cls.objects.get(course_key=course_key).enabled
         except cls.DoesNotExist:
             return False
+
+
+@receiver(models.signals.post_save, sender=VerifiedTrackCohortedCourse)
+@receiver(models.signals.post_delete, sender=VerifiedTrackCohortedCourse)
+def invalidate_verified_track_cache(sender, **kwargs):   # pylint: disable=unused-argument
+    """Invalidate the cache of VerifiedTrackCohortedCourse. """
+    RequestCache.clear_request_cache(name=VerifiedTrackCohortedCourse.CACHE_NAMESPACE)