Backend: Add composite index to LeaderboardData model for query optimization (#4989)

Author: RishabhJain2018

apps/challenges/migrations/0116_leaderboard_data_leaderboard_query_index.py

@@ -0,0 +1,23 @@
+# Generated by Django 2.2.20 on 2026-02-06 03:35
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        (
+            "challenges",
+            "0115_add_show_scores_on_leaderboard_to_challenge_phase_split",
+        ),
+    ]
+
+    operations = [
+        migrations.AddIndex(
+            model_name="leaderboarddata",
+            index=models.Index(
+                fields=["challenge_phase_split", "is_disabled", "-created_at"],
+                name="ld_chphase_isdisc_created_idx",
+            ),
+        ),
+    ]

apps/challenges/models.py

@@ -573,6 +573,12 @@ def __str__(self):
     class Meta:
         app_label = "challenges"
         db_table = "leaderboard_data"
+        indexes = [
+            models.Index(
+                fields=["challenge_phase_split", "is_disabled", "-created_at"],
+                name="ld_chphase_isdisc_created_idx",
+            ),
+        ]
 
 
 class ChallengeConfiguration(TimeStampedModel):

tests/unit/challenges/test_models.py

@@ -272,3 +272,26 @@ def test__str__(self):
             "{0} : {1}".format(self.challenge_phase_split, self.submission),
             self.leaderboard_data.__str__(),
         )
+
+    def test_leaderboard_query_index_exists(self):
+        """
+        Verify LeaderboardData has the composite index for leaderboard query
+        optimization (EVALAI-HY8). The index supports filtering by
+        challenge_phase_split, is_disabled and ordering by created_at DESC.
+        """
+        index_names = [idx.name for idx in LeaderboardData._meta.indexes]
+        self.assertIn(
+            "ld_chphase_isdisc_created_idx",
+            index_names,
+            "LeaderboardData should have ld_chphase_isdisc_created_idx index",
+        )
+        index = next(
+            idx
+            for idx in LeaderboardData._meta.indexes
+            if idx.name == "ld_chphase_isdisc_created_idx"
+        )
+        self.assertEqual(
+            index.fields,
+            ["challenge_phase_split", "is_disabled", "-created_at"],
+            "Index should cover challenge_phase_split, is_disabled, created_at DESC",
+        )