From 6bdde42a8f4436d0beb88c35d40975c138ea83c4 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Wed, 27 Oct 2021 11:58:59 +0100
Subject: [PATCH 1/2] Fix thread BG update to not seq scan event_json

For some reason the query optimiser decided to seq scan both tables,
rather than index scanning `event_json`.
---
 synapse/storage/databases/main/events_bg_updates.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/synapse/storage/databases/main/events_bg_updates.py b/synapse/storage/databases/main/events_bg_updates.py
index f92d82487656..ae3a8a63e42f 100644
--- a/synapse/storage/databases/main/events_bg_updates.py
+++ b/synapse/storage/databases/main/events_bg_updates.py
@@ -1108,7 +1108,7 @@ def _event_thread_relation_txn(txn: LoggingTransaction) -> int:
                 """
                 SELECT event_id, json FROM event_json
                 LEFT JOIN event_relations USING (event_id)
-                WHERE event_id > ? AND relates_to_id IS NULL
+                WHERE event_id > ? AND event_relations.event_id IS NULL
                 ORDER BY event_id LIMIT ?
                 """,
                 (last_event_id, batch_size),

From 5eaf65d970c5a1c07a9b18d13b244f68df3adc67 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Wed, 27 Oct 2021 12:01:14 +0100
Subject: [PATCH 2/2] Newsfile

---
 changelog.d/11192.feature | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/11192.feature

diff --git a/changelog.d/11192.feature b/changelog.d/11192.feature
new file mode 100644
index 000000000000..76b0d280845e
--- /dev/null
+++ b/changelog.d/11192.feature
@@ -0,0 +1 @@
+Experimental support for the thread relation defined in [MSC3440](https://github.com/matrix-org/matrix-doc/pull/3440).