From bc6d71d4de8a3f6a430ca084419e079f2e3ecf31 Mon Sep 17 00:00:00 2001
From: David Sanders <shang.xiao.sanders@gmail.com>
Date: Fri, 22 Sep 2023 19:21:37 +1000
Subject: [PATCH] [5.0.x] Fixed #34825 -- Avoided setting unused connections
 when initializing parallel workers.

Backport of a5905b164dbf52e59fa646af9c3d523c0804d86a from main
---
 django/test/runner.py      | 7 ++++++-
 tests/test_runner/tests.py | 3 ++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/django/test/runner.py b/django/test/runner.py
index 3a30674b61..eb3cea1959 100644
--- a/django/test/runner.py
+++ b/django/test/runner.py
@@ -406,6 +406,7 @@ def _init_worker(
     process_setup=None,
     process_setup_args=None,
     debug_mode=None,
+    used_aliases=None,
 ):
     """
     Switch to databases dedicated to this worker.
@@ -430,7 +431,8 @@ def _init_worker(
         django.setup()
         setup_test_environment(debug=debug_mode)
 
-    for alias in connections:
+    db_aliases = used_aliases or connections
+    for alias in db_aliases:
         connection = connections[alias]
         if start_method == "spawn":
             # Restore initial settings in spawned processes.
@@ -491,6 +493,7 @@ class ParallelTestSuite(unittest.TestSuite):
         self.buffer = buffer
         self.initial_settings = None
         self.serialized_contents = None
+        self.used_aliases = None
         super().__init__()
 
     def run(self, result):
@@ -520,6 +523,7 @@ class ParallelTestSuite(unittest.TestSuite):
                 self.process_setup.__func__,
                 self.process_setup_args,
                 self.debug_mode,
+                self.used_aliases,
             ],
         )
         args = [
@@ -1052,6 +1056,7 @@ class DiscoverRunner:
         suite.serialized_aliases = set(
             alias for alias, serialize in databases.items() if serialize
         )
+        suite.used_aliases = set(databases)
         with self.time_keeper.timed("Total database setup"):
             old_config = self.setup_databases(
                 aliases=databases,
diff --git a/tests/test_runner/tests.py b/tests/test_runner/tests.py
index 25b7f40e99..569fd7e862 100644
--- a/tests/test_runner/tests.py
+++ b/tests/test_runner/tests.py
@@ -748,8 +748,9 @@ class TestRunnerInitializerTests(SimpleTestCase):
         # Initializer must be a function.
         self.assertIs(mocked_pool.call_args.kwargs["initializer"], _init_worker)
         initargs = mocked_pool.call_args.kwargs["initargs"]
-        self.assertEqual(len(initargs), 6)
+        self.assertEqual(len(initargs), 7)
         self.assertEqual(initargs[5], True)  # debug_mode
+        self.assertEqual(initargs[6], {db.DEFAULT_DB_ALIAS})  # Used database aliases.
 
 
 class Ticket17477RegressionTests(AdminScriptTestCase):