Clean up existing indices on Upload (aka ReportSession)

shared/django_apps/reports/migrations/0035_upload_indices_part2.py

@@ -0,0 +1,43 @@
+# Generated by Django 4.2.16 on 2024-11-28 12:37
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+    atomic = False
+
+    dependencies = [
+        ("reports", "0034_upload_indices_part1"),
+    ]
+
+    operations = [
+        migrations.SeparateDatabaseAndState(
+            state_operations=[
+                migrations.RemoveIndex(
+                    model_name="reportsession",
+                    name="upload_index_id_type_number",
+                ),
+            ],
+            database_operations=[
+                # We drop these indices for the following reasons:
+                # - `upload_index_id_type_number`: This matches the above state migration,
+                #   and it looks like the index does not actually exist in the production DB.
+                # The following indices exist in the production DB, but not in django state/migrations:
+                # - `reports_upload_order_number_upload_type_report_id_index`:
+                #   This index actually has the *reverse* order that the one above, which means that frequent updates
+                #   to the `order_number` lead to a lot of costly index updates.
+                # - `reports_upload_report_id_f6b4ffae`: Queries on `report_id` should already been covered by the
+                #    newly added index on `report_id`+`upload_type`.
+                # - `reports_upload_created_at_index`: We never query by `created_at` directly. The only place where we
+                #   use this is in an `ORDER BY` that is already covered by the `report_id`.
+                migrations.RunSQL(
+                    sql="""
+                    DROP INDEX CONCURRENTLY IF EXISTS "upload_index_id_type_number";
+                    DROP INDEX CONCURRENTLY IF EXISTS "reports_upload_order_number_upload_type_report_id_index";
+                    DROP INDEX CONCURRENTLY IF EXISTS "reports_upload_report_id_f6b4ffae";
+                    DROP INDEX CONCURRENTLY IF EXISTS "reports_upload_created_at_index";
+                """
+                ),
+            ],
+        )
+    ]

shared/django_apps/reports/models.py

@@ -202,11 +202,6 @@ class Meta:
                 name="upload_report_type_idx",
                 fields=["report_id", "upload_type"],
             ),
-            # TODO(swatinem): remove the index below in a followup migration:
-            models.Index(
-                name="upload_index_id_type_number",
-                fields=["report_id", "upload_type", "order_number"],
-            ),
         ]
 
     @property