Speed up slow initial sliding syncs on large servers (#17946)

This was due to a missing index, which meant that deleting previous
connections associated with the device and `conn_id` took a long time.

1 files changed, 20 insertions, 0 deletions

diff --git a/synapse/storage/schema/main/delta/88/05_sliding_sync_room_config_index.sql b/synapse/storage/schema/main/delta/88/05_sliding_sync_room_config_index.sql
new file mode 100644

index 0000000000..7b2e18a84b
--- /dev/null
+++ b/synapse/storage/schema/main/delta/88/05_sliding_sync_room_config_index.sql
@@ -0,0 +1,20 @@
+--
+-- This file is licensed under the Affero General Public License (AGPL) version 3.
+--
+-- Copyright (C) 2024 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 an index on sliding_sync_connection_room_configs(required_state_id), so
+-- that when we delete entries in `sliding_sync_connection_required_state` it's
+-- efficient for Postgres to check they've been deleted from
+-- `sliding_sync_connection_room_configs` too
+INSERT INTO background_updates (ordering, update_name, progress_json) VALUES
+    (8805, 'sliding_sync_connection_room_configs_required_state_id_idx', '{}');