Revert the background job to clear unreferenced state groups (that was introduced in v1.126.0rc1), due to a suspected issue that causes increased disk usage. (#18222)

Revert "Add background job to clear unreferenced state groups (#18154)"

This mechanism is suspected of inserting large numbers of rows into
`state_groups_state`,
thus unreasonably increasing disk usage.

See: https://github.com/element-hq/synapse/issues/18217

This reverts commit 5121f9210c989fcc909e78195133876dff3bc9b9 (#18154).

---------

Signed-off-by: Olivier 'reivilibre <oliverw@matrix.org>

2 files changed, 0 insertions, 17 deletions

diff --git a/synapse/storage/schema/__init__.py b/synapse/storage/schema/__init__.py

index c90c2c6051..49e648a92f 100644
--- a/synapse/storage/schema/__init__.py
+++ b/synapse/storage/schema/__init__.py
@@ -158,7 +158,6 @@ Changes in SCHEMA_VERSION = 88
 
 Changes in SCHEMA_VERSION = 89
     - Add `state_groups_pending_deletion` and `state_groups_persisting` tables.
-    - Add background update to delete unreferenced state groups.
 """
 
 
diff --git a/synapse/storage/schema/state/delta/89/02_delete_unreferenced_state_groups.sql b/synapse/storage/schema/state/delta/89/02_delete_unreferenced_state_groups.sql
deleted file mode 100644

index 184dc8564c..0000000000
--- a/synapse/storage/schema/state/delta/89/02_delete_unreferenced_state_groups.sql
+++ /dev/null
@@ -1,16 +0,0 @@
---
--- This file is licensed under the Affero General Public License (AGPL) version 3.
---
--- Copyright (C) 2025 New Vector, Ltd
---
--- This program is free software: you can redistribute it and/or modify
--- it under the terms of the GNU Affero General Public License as
--- published by the Free Software Foundation, either version 3 of the
--- License, or (at your option) any later version.
---
--- See the GNU Affero General Public License for more details:
--- <https://www.gnu.org/licenses/agpl-3.0.html>.
-
--- Add a background update to delete any unreferenced state groups
-INSERT INTO background_updates (ordering, update_name, progress_json) VALUES
-  (8902, 'delete_unreferenced_state_groups_bg_update', '{}');