fix: Add composite index to code references to improve query performance (#6835)

Author: matthewelwell

api/projects/code_references/migrations/0002_add_project_repo_created_index.py

@@ -0,0 +1,32 @@
+from django.db import migrations, models
+
+from core.migration_helpers import PostgresOnlyRunSQL
+
+
+class Migration(migrations.Migration):
+
+    atomic = False
+
+    dependencies = [
+        ("code_references", "0001_code_references"),
+    ]
+
+    operations = [
+        migrations.SeparateDatabaseAndState(
+            state_operations=[
+                migrations.AddIndex(
+                    model_name="featureflagcodereferencesscan",
+                    index=models.Index(
+                        fields=["project", "repository_url", "-created_at"],
+                        name="code_ref_proj_repo_created_idx",
+                    ),
+                ),
+            ],
+            database_operations=[
+                PostgresOnlyRunSQL(
+                    'CREATE INDEX CONCURRENTLY IF NOT EXISTS "code_ref_proj_repo_created_idx" ON "code_references_featureflagcodereferencesscan" ("project_id", "repository_url", "created_at" DESC);',
+                    reverse_sql='DROP INDEX CONCURRENTLY IF EXISTS "code_ref_proj_repo_created_idx"',
+                ),
+            ],
+        ),
+    ]

api/projects/code_references/models.py

@@ -29,3 +29,9 @@ class FeatureFlagCodeReferencesScan(models.Model):
 
     class Meta:
         ordering = ["-created_at"]
+        indexes = [
+            models.Index(
+                fields=["project", "repository_url", "-created_at"],
+                name="code_ref_proj_repo_created_idx",
+            ),
+        ]