From 15a11ad4f80a01f8e1893e94e81dc2f12494612c Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Thu, 25 Aug 2022 15:41:26 -0400
Subject: [PATCH 1/3] Use execute_values instead of execute_batch when
 inserting into the event_push_actions_staging table.

---
 synapse/storage/databases/main/event_push_actions.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/synapse/storage/databases/main/event_push_actions.py b/synapse/storage/databases/main/event_push_actions.py
index 8dfa545c2771..6e3619450966 100644
--- a/synapse/storage/databases/main/event_push_actions.py
+++ b/synapse/storage/databases/main/event_push_actions.py
@@ -707,15 +707,16 @@ def _add_push_actions_to_staging_txn(txn: LoggingTransaction) -> None:
             sql = """
                 INSERT INTO event_push_actions_staging
                     (event_id, user_id, actions, notif, highlight, unread)
-                VALUES (?, ?, ?, ?, ?, ?)
+                VALUES ?
             """
 
-            txn.execute_batch(
+            txn.execute_values(
                 sql,
                 (
                     _gen_entry(user_id, actions)
                     for user_id, actions in user_id_actions.items()
                 ),
+                fetch=False,
             )
 
         return await self.db_pool.runInteraction(

From ac69e5c3a65b4c9d54d916e29c70414d10536918 Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Thu, 25 Aug 2022 15:46:22 -0400
Subject: [PATCH 2/3] Use the simpler_insert_many helper.

---
 .../databases/main/event_push_actions.py      | 29 +++++--------------
 1 file changed, 8 insertions(+), 21 deletions(-)

diff --git a/synapse/storage/databases/main/event_push_actions.py b/synapse/storage/databases/main/event_push_actions.py
index 6e3619450966..9f410d69def5 100644
--- a/synapse/storage/databases/main/event_push_actions.py
+++ b/synapse/storage/databases/main/event_push_actions.py
@@ -700,27 +700,14 @@ def _gen_entry(
                 int(count_as_unread),  # unread column
             )
 
-        def _add_push_actions_to_staging_txn(txn: LoggingTransaction) -> None:
-            # We don't use simple_insert_many here to avoid the overhead
-            # of generating lists of dicts.
-
-            sql = """
-                INSERT INTO event_push_actions_staging
-                    (event_id, user_id, actions, notif, highlight, unread)
-                VALUES ?
-            """
-
-            txn.execute_values(
-                sql,
-                (
-                    _gen_entry(user_id, actions)
-                    for user_id, actions in user_id_actions.items()
-                ),
-                fetch=False,
-            )
-
-        return await self.db_pool.runInteraction(
-            "add_push_actions_to_staging", _add_push_actions_to_staging_txn
+        await self.db_pool.simple_insert_many(
+            "event_push_actions_staging",
+            keys=("event_id", "user_id", "actions", "notif", "highlight", "unread"),
+            values=[
+                _gen_entry(user_id, actions)
+                for user_id, actions in user_id_actions.items()
+            ],
+            desc="add_push_actions_to_staging",
         )
 
     async def remove_push_actions_from_staging(self, event_id: str) -> None:

From 691bfa30d16211a2ddb3260378c2aff142777421 Mon Sep 17 00:00:00 2001
From: Patrick Cloke <patrickc@matrix.org>
Date: Thu, 25 Aug 2022 15:47:29 -0400
Subject: [PATCH 3/3] Newsfragment

---
 changelog.d/13634.feature | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/13634.feature

diff --git a/changelog.d/13634.feature b/changelog.d/13634.feature
new file mode 100644
index 000000000000..0a8827205d7b
--- /dev/null
+++ b/changelog.d/13634.feature
@@ -0,0 +1 @@
+Improve performance of sending messages in rooms with thousands of local users.