See etianen#885: Very slow VersionQuerySet.get_deleted

Version model: add index on (content_type, db).
VersionQuerySet.get_deleted: filter by content_type and db before subquery to increase performance.

reversion/migrations/0002_add_index_on_version_for_content_type_and_db.py

@@ -0,0 +1,17 @@
+# Generated by Django 3.2.6 on 2021-08-16 18:08
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('reversion', '0001_squashed_0004_auto_20160611_1202'),
+    ]
+
+    operations = [
+        migrations.AddIndex(
+            model_name='version',
+            index=models.Index(fields=['content_type', 'db'], name='reversion_v_content_f95daf_idx'),
+        ),
+    ]

reversion/models.py

@@ -189,7 +189,8 @@ def get_deleted(self, model, model_db=None):
                 latest_pk=models.Max("pk")
             ).order_by().values_list("latest_pk", flat=True)
         # Perform the subquery.
-        return self.filter(pk__in=subquery)
+        # Filter by model to reduce query execution time.
+        return self.get_for_model(model, model_db=model_db).filter(pk__in=subquery)
 
     def get_unique(self):
         last_key = None
@@ -328,6 +329,11 @@ class Meta:
         unique_together = (
             ("db", "content_type", "object_id", "revision"),
         )
+        indexes = (
+            models.Index(
+                fields=("content_type", "db")
+            ),
+        )
         ordering = ("-pk",)