[PATCH 08/11] Add covering index to patchwork_submissions for /list/ queries

[Stewart Smith]

This gets PostgreSQL to generate *much* better query plans, gaining us
about two orders of magnitude in performance on the /list/ query for the
worst state project on the patchwork.ozlabs.org instance (qemu-devel).

Signed-off-by: Stewart Smith <stewart at linux.ibm.com>
---
 .../0029_add_submission_covering_index.py     | 19 +++++++++++++++++++
 patchwork/models.py                           |  8 ++++++++
 2 files changed, 27 insertions(+)
 create mode 100644 patchwork/migrations/0029_add_submission_covering_index.py

diff --git a/patchwork/migrations/0029_add_submission_covering_index.py b/patchwork/migrations/0029_add_submission_covering_index.py
new file mode 100644
index 000000000000..064f2ac4ae9d
--- /dev/null
+++ b/patchwork/migrations/0029_add_submission_covering_index.py
@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.15 on 2018-08-10 16:15
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('patchwork', '0028_add_list_covering_index'),
+    ]
+
+    operations = [
+        migrations.AddIndex(
+            model_name='submission',
+            index=models.Index(fields=['date', 'project', 'submitter', 'name'], name='submission_covering_idx'),
+        ),
+    ]
diff --git a/patchwork/models.py b/patchwork/models.py
index d356a6379ac3..7a8d363c4652 100644
--- a/patchwork/models.py
+++ b/patchwork/models.py
@@ -389,6 +389,14 @@ class Submission(FilenameMixin, EmailMixin, models.Model):
     class Meta:
         ordering = ['date']
         unique_together = [('msgid', 'project')]
+        indexes = [
+            # This is a covering index for the /list/ query
+            # Like what we have for Patch, but used for displaying what we want
+            # rather than for working out the count
+            # (of course, this all depends on the SQL optimiser of your db engine)
+            models.Index(fields=['date','project','submitter','name'],
+                         name='submission_covering_idx'),
+            ]
 
 
 class SeriesMixin(object):
-- 
2.17.1