Lower minumum batch size to 1 for background updates (#11422)

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

changelog.d/11422.bugfix

@@ -0,0 +1 @@
+Improve performance of various background database schema updates.

synapse/storage/background_updates.py

@@ -82,7 +82,7 @@ class BackgroundUpdater:
     process and autotuning the batch size.
     """
 
-    MINIMUM_BACKGROUND_BATCH_SIZE = 100
+    MINIMUM_BACKGROUND_BATCH_SIZE = 1
     DEFAULT_BACKGROUND_BATCH_SIZE = 100
     BACKGROUND_UPDATE_INTERVAL_MS = 1000
     BACKGROUND_UPDATE_DURATION_MS = 100

tests/rest/admin/test_background_updates.py

@@ -20,6 +20,7 @@ import synapse.rest.admin
 from synapse.api.errors import Codes
 from synapse.rest.client import login
 from synapse.server import HomeServer
+from synapse.storage.background_updates import BackgroundUpdater
 
 from tests import unittest
 
@@ -150,9 +151,11 @@ class BackgroundUpdatesTestCase(unittest.HomeserverTestCase):
                 "current_updates": {
                     "master": {
                         "name": "test_update",
-                        "average_items_per_ms": 0.1,
+                        "average_items_per_ms": 0.001,
                         "total_duration_ms": 1000.0,
-                        "total_item_count": 100,
+                        "total_item_count": (
+                            BackgroundUpdater.MINIMUM_BACKGROUND_BATCH_SIZE
+                        ),
                     }
                 },
                 "enabled": True,
@@ -203,9 +206,11 @@ class BackgroundUpdatesTestCase(unittest.HomeserverTestCase):
                 "current_updates": {
                     "master": {
                         "name": "test_update",
-                        "average_items_per_ms": 0.1,
+                        "average_items_per_ms": 0.001,
                         "total_duration_ms": 1000.0,
-                        "total_item_count": 100,
+                        "total_item_count": (
+                            BackgroundUpdater.MINIMUM_BACKGROUND_BATCH_SIZE
+                        ),
                     }
                 },
                 "enabled": False,
@@ -230,9 +235,11 @@ class BackgroundUpdatesTestCase(unittest.HomeserverTestCase):
                 "current_updates": {
                     "master": {
                         "name": "test_update",
-                        "average_items_per_ms": 0.1,
+                        "average_items_per_ms": 0.001,
                         "total_duration_ms": 1000.0,
-                        "total_item_count": 100,
+                        "total_item_count": (
+                            BackgroundUpdater.MINIMUM_BACKGROUND_BATCH_SIZE
+                        ),
                     }
                 },
                 "enabled": False,
@@ -267,9 +274,11 @@ class BackgroundUpdatesTestCase(unittest.HomeserverTestCase):
                 "current_updates": {
                     "master": {
                         "name": "test_update",
-                        "average_items_per_ms": 0.1,
+                        "average_items_per_ms": 0.001,
                         "total_duration_ms": 2000.0,
-                        "total_item_count": 200,
+                        "total_item_count": (
+                            2 * BackgroundUpdater.MINIMUM_BACKGROUND_BATCH_SIZE
+                        ),
                     }
                 },
                 "enabled": True,

tests/storage/test_background_update.py

@@ -19,11 +19,11 @@ class BackgroundUpdateTestCase(unittest.HomeserverTestCase):
         )
 
     def test_do_background_update(self):
-        # the time we claim each update takes
-        duration_ms = 42
+        # the time we claim it takes to update one item when running the update
+        duration_ms = 4200
 
         # the target runtime for each bg update
-        target_background_update_duration_ms = 50000
+        target_background_update_duration_ms = 5000000
 
         store = self.hs.get_datastore()
         self.get_success(
@@ -57,7 +57,7 @@ class BackgroundUpdateTestCase(unittest.HomeserverTestCase):
 
         # on the first call, we should get run with the default background update size
         self.update_handler.assert_called_once_with(
-            {"my_key": 1}, self.updates.DEFAULT_BACKGROUND_BATCH_SIZE
+            {"my_key": 1}, self.updates.MINIMUM_BACKGROUND_BATCH_SIZE
         )
 
         # second step: complete the update