From 83ef828a71864739718ef0d3a50b89d17e7024cb Mon Sep 17 00:00:00 2001
From: Gorka Eguileor <geguileo@redhat.com>
Date: Fri, 14 Jul 2023 13:13:15 +0200
Subject: [PATCH] Scheduler: Remove unnecessary DB read

The scheduler has been receiving the whole volume object for a while
now instead of just the volume id, so during a volume creation operation
the scheduler doesn't need to read the whole volume from the database.

This patch skips a DB read when the volume is present in the
request_spec, speeding up the volume creation code in the scheduler,
reducing network traffic, and load on the DBMS.

Change-Id: Ifd3c817d8c6be9ae9d2ff15f4e1dccd969eca7e9
---
 cinder/scheduler/driver.py                    |  5 +++--
 cinder/scheduler/filter_scheduler.py          |  3 ++-
 cinder/tests/unit/scheduler/test_scheduler.py | 17 +++++++++++++++++
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/cinder/scheduler/driver.py b/cinder/scheduler/driver.py
index fe92905bee2..6e7ecf6e6f1 100644
--- a/cinder/scheduler/driver.py
+++ b/cinder/scheduler/driver.py
@@ -42,12 +42,13 @@ CONF.register_opts(scheduler_driver_opts)
 
 
 def volume_update_db(context, volume_id, host, cluster_name,
-                     availability_zone=None):
+                     availability_zone=None, volume=None):
     """Set the host, cluster_name, and set the scheduled_at field of a volume.
 
     :returns: A Volume with the updated fields set properly.
     """
-    volume = objects.Volume.get_by_id(context, volume_id)
+    if not volume:
+        volume = objects.Volume.get_by_id(context, volume_id)
     volume.host = host
     volume.cluster_name = cluster_name
     volume.scheduled_at = timeutils.utcnow()
diff --git a/cinder/scheduler/filter_scheduler.py b/cinder/scheduler/filter_scheduler.py
index db53196e8c0..9edf6c3e04b 100644
--- a/cinder/scheduler/filter_scheduler.py
+++ b/cinder/scheduler/filter_scheduler.py
@@ -110,7 +110,8 @@ class FilterScheduler(driver.Scheduler):
             context, volume_id,
             backend.host,
             backend.cluster_name,
-            availability_zone=backend.service['availability_zone'])
+            availability_zone=backend.service['availability_zone'],
+            volume=request_spec.get('volume'))
         self._post_select_populate_filter_properties(filter_properties,
                                                      backend)
 
diff --git a/cinder/tests/unit/scheduler/test_scheduler.py b/cinder/tests/unit/scheduler/test_scheduler.py
index c2c51a0c1e0..f0c8fdecbbd 100644
--- a/cinder/tests/unit/scheduler/test_scheduler.py
+++ b/cinder/tests/unit/scheduler/test_scheduler.py
@@ -716,6 +716,23 @@ class SchedulerDriverModuleTestCase(test.TestCase):
         driver.volume_update_db(self.context, volume.id, 'fake_host',
                                 'fake_cluster')
         scheduled_at = volume.scheduled_at.replace(tzinfo=None)
+        _mock_volume_get.assert_called_once_with(self.context, volume.id)
+        _mock_vol_update.assert_called_once_with(
+            self.context, volume.id, {'host': 'fake_host',
+                                      'cluster_name': 'fake_cluster',
+                                      'scheduled_at': scheduled_at,
+                                      'availability_zone': None})
+
+    @mock.patch('cinder.db.volume_update')
+    @mock.patch('cinder.objects.volume.Volume.get_by_id')
+    def test_volume_host_update_db_vol_present(self, _mock_volume_get,
+                                               _mock_vol_update):
+        volume = fake_volume.fake_volume_obj(self.context, use_quota=True)
+
+        driver.volume_update_db(self.context, volume.id, 'fake_host',
+                                'fake_cluster', volume=volume)
+        scheduled_at = volume.scheduled_at.replace(tzinfo=None)
+        _mock_volume_get.assert_not_called()
         _mock_vol_update.assert_called_once_with(
             self.context, volume.id, {'host': 'fake_host',
                                       'cluster_name': 'fake_cluster',