Revert "add index for modified to course and subsection grades"

lms/djangoapps/grades/migrations/0009_auto_20170111_1507.py

-# -*- coding: utf-8 -*-
-from __future__ import unicode_literals
-
-from django.db import migrations, models
-
-
-class Migration(migrations.Migration):
-
-    dependencies = [
-        ('grades', '0008_persistentsubsectiongrade_first_attempted'),
-    ]
-
-    operations = [
-        migrations.AlterIndexTogether(
-            name='persistentcoursegrade',
-            index_together=set([('passed_timestamp', 'course_id'), ('modified', 'course_id')]),
-        ),
-        migrations.AlterIndexTogether(
-            name='persistentsubsectiongrade',
-            index_together=set([('modified', 'course_id', 'usage_key')]),
-        ),
-    ]

lms/djangoapps/grades/models.py

@@ -253,14 +253,6 @@ class PersistentSubsectionGrade(DeleteGradesMixin, TimeStampedModel):
             # * Course staff can see all grades for a course using (course_id,)
             ('course_id', 'user_id', 'usage_key'),
         ]
-        # Allows querying in the following ways:
-        # (modified): find all the grades updated within a certain timespan
-        # (modified, course_id): find all the grades updated within a timespan for a certain course
-        # (modified, course_id, usage_key): find all the grades updated within a timespan for a subsection
-        #   in a course
-        index_together = [
-            ('modified', 'course_id', 'usage_key')
-        ]
 
     # primary key will need to be large for this table
     id = UnsignedBigIntAutoField(primary_key=True)  # pylint: disable=invalid-name
@@ -510,14 +502,11 @@ class PersistentCourseGrade(DeleteGradesMixin, TimeStampedModel):
         # (course_id) for instructors to see all course grades, implicitly created via the unique_together constraint
         # (user_id) for course dashboard; explicitly declared as an index below
         # (passed_timestamp, course_id) for tracking when users first earned a passing grade.
-        # (modified): find all the grades updated within a certain timespan
-        # (modified, course_id): find all the grades updated within a certain timespan for a course
         unique_together = [
             ('course_id', 'user_id'),
         ]
         index_together = [
             ('passed_timestamp', 'course_id'),
-            ('modified', 'course_id')
         ]
 
     # primary key will need to be large for this table