views: Add a new covering index for patch table

The new index uses project_id as the first key. This is important, as it
seems that almost all web queries filter over project_id. This index
indexes over descending submission date, as this is the default sorting
for the patches list.

Author: fstachura

patchwork/migrations/0049_patch_patch_covering_idx_default.py

@@ -0,0 +1,19 @@
+# Generated by Django 6.0.6 on 2026-08-13 00:14
+
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('patchwork', '0048_series_dependencies'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.AddIndex(
+            model_name='patch',
+            index=models.Index(fields=['project', 'archived', 'state', '-date', 'delegate', 'submitter'], name='patch_covering_idx_default'),
+        ),
+    ]

patchwork/models.py

@@ -735,6 +735,17 @@ class Meta:
                 ],
                 name='patch_covering_idx',
             ),
+            models.Index(
+                fields=[
+                    'project',
+                    'archived',
+                    'state',
+                    '-date',
+                    'delegate',
+                    'submitter',
+                ],
+                name='patch_covering_idx_default',
+            ),
         ]