Add indexes for quarantined media lookups

synapse/storage/databases/main/media_repository.py

@@ -177,6 +177,35 @@ class MediaRepositoryBackgroundUpdateStore(SQLBaseStore):
             ],
         )
 
+        self.db_pool.updates.register_background_index_update(
+            update_name="local_media_repository_quarantined_ts_idx",
+            index_name="local_media_repository_quarantined_by_quarantined_ts_media_id",
+            table="local_media_repository",
+            where_clause="quarantined_by IS NOT NULL",
+            columns=[
+                # We include columns in both the WHERE and ORDER BY clauses to make
+                # the resulting query a bit more efficient.
+                "quarantined_by",
+                "quarantined_ts",
+                "media_id",
+            ],
+        )
+
+        self.db_pool.updates.register_background_index_update(
+            update_name="remote_media_cache_quarantined_ts_idx",
+            index_name="remote_media_cache_quarantined_by_quarantined_ts_media_origin_media_id",
+            table="remote_media_cache",
+            where_clause="quarantined_by IS NOT NULL",
+            columns=[
+                # We include columns in both the WHERE and ORDER BY clauses to make
+                # the resulting query a bit more efficient.
+                "quarantined_by",
+                "quarantined_ts",
+                "media_origin",
+                "media_id",
+            ],
+        )
+
         self.db_pool.updates.register_background_update_handler(
             BG_UPDATE_REMOVE_MEDIA_REPO_INDEX_WITHOUT_METHOD_2,
             self._drop_media_index_without_method,

synapse/storage/databases/main/room.py

@@ -969,6 +969,11 @@ class RoomWorkerStore(CacheInvalidationWorkerStore):
         ) -> list[str]:
             # We order by quarantined timestamp *and* media ID (including origin, when
             # known) to ensure the ordering is stable for established servers.
+            #
+            # Note: these queries are backed by indexes. If the queries change, update
+            # them:
+            # - local_media_repository_quarantined_by_quarantined_ts_media_id
+            # - remote_media_cache_quarantined_by_quarantined_ts_media_origin_media_id
             if local:
                 sql = "SELECT '' as media_origin, media_id FROM local_media_repository WHERE quarantined_by IS NOT NULL ORDER BY quarantined_ts, media_id ASC LIMIT ? OFFSET ?"
             else:

synapse/storage/schema/main/delta/93/04_add_quarantined_ts_to_media.sql

@@ -23,5 +23,4 @@ ALTER TABLE remote_media_cache ADD COLUMN quarantined_ts BIGINT;
 UPDATE local_media_repository SET quarantined_ts = 0 WHERE quarantined_by IS NOT NULL;
 UPDATE remote_media_cache SET quarantined_ts = 0 WHERE quarantined_by IS NOT NULL;
 
--- Note: We *probably* should have an index on quarantined_ts, but we're going
--- to try to defer that to a future migration after seeing the performance impact.
+-- Note: the index is added in 05_add_quarantined_by_index.sql

synapse/storage/schema/main/delta/93/05_quarantined_ts_index.sql

@@ -0,0 +1,18 @@
+--
+-- This file is licensed under the Affero General Public License (AGPL) version 3.
+--
+-- Copyright (C) 2025 Element Creations, 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>.
+
+INSERT INTO background_updates (ordering, update_name, progress_json) VALUES
+  -- we should start at ordering 9305, but there's higher conflict if we steal 9306's ordering, so
+  -- we'll steal 9304's ordering instead. 9304 is where the applicable columns were added.
+  (9304, 'local_media_repository_quarantined_ts_idx', '{}'),
+  (9305, 'remote_media_cache_quarantined_ts_idx', '{}');