diff --git a/synapse/storage/databases/main/event_push_actions.py b/synapse/storage/databases/main/event_push_actions.py
index 9c6deb56b95e..3494a40d896c 100644
--- a/synapse/storage/databases/main/event_push_actions.py
+++ b/synapse/storage/databases/main/event_push_actions.py
@@ -773,9 +773,11 @@ async def add_push_actions_to_staging(
 
         # This is a helper function for generating the necessary tuple that
         # can be used to insert into the `event_push_actions_staging` table.
+        #
+        # TODO(threads): Return the event's thread_id instead of hard-coding main.
         def _gen_entry(
             user_id: str, actions: Collection[Union[Mapping, str]]
-        ) -> Tuple[str, str, str, int, int, int]:
+        ) -> Tuple[str, str, str, int, int, int, str]:
             is_highlight = 1 if _action_has_highlight(actions) else 0
             notif = 1 if "notify" in actions else 0
             return (
@@ -785,11 +787,20 @@ def _gen_entry(
                 notif,  # notif column
                 is_highlight,  # highlight column
                 int(count_as_unread),  # unread column
+                "main",  # thread_id column
             )
 
         await self.db_pool.simple_insert_many(
             "event_push_actions_staging",
-            keys=("event_id", "user_id", "actions", "notif", "highlight", "unread"),
+            keys=(
+                "event_id",
+                "user_id",
+                "actions",
+                "notif",
+                "highlight",
+                "unread",
+                "thread_id",
+            ),
             values=[
                 _gen_entry(user_id, actions)
                 for user_id, actions in user_id_actions.items()
@@ -1070,6 +1081,8 @@ def _handle_new_receipts_for_notifs_txn(self, txn: LoggingTransaction) -> bool:
             )
 
             # Replace the previous summary with the new counts.
+            #
+            # TODO(threads): Upsert per-thread instead of setting them all to main.
             self.db_pool.simple_upsert_txn(
                 txn,
                 table="event_push_summary",
@@ -1079,6 +1092,7 @@ def _handle_new_receipts_for_notifs_txn(self, txn: LoggingTransaction) -> bool:
                     "unread_count": unread_count,
                     "stream_ordering": old_rotate_stream_ordering,
                     "last_receipt_stream_ordering": stream_ordering,
+                    "thread_id": "main",
                 },
             )
 
@@ -1227,17 +1241,19 @@ def _rotate_notifs_before_txn(
 
         logger.info("Rotating notifications, handling %d rows", len(summaries))
 
+        # TODO(threads): Update on a per-thread basis.
         self.db_pool.simple_upsert_many_txn(
             txn,
             table="event_push_summary",
             key_names=("user_id", "room_id"),
             key_values=[(user_id, room_id) for user_id, room_id in summaries],
-            value_names=("notif_count", "unread_count", "stream_ordering"),
+            value_names=("notif_count", "unread_count", "stream_ordering", "thread_id"),
             value_values=[
                 (
                     summary.notif_count,
                     summary.unread_count,
                     summary.stream_ordering,
+                    "main",
                 )
                 for summary in summaries.values()
             ],
diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py
index a4010ee28dca..c0b4080e4b3d 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -2192,9 +2192,9 @@ def _set_push_actions_for_event_and_users_txn(
         sql = """
             INSERT INTO event_push_actions (
                 room_id, event_id, user_id, actions, stream_ordering,
-                topological_ordering, notif, highlight, unread
+                topological_ordering, notif, highlight, unread, thread_id
             )
-            SELECT ?, event_id, user_id, actions, ?, ?, notif, highlight, unread
+            SELECT ?, event_id, user_id, actions, ?, ?, notif, highlight, unread, thread_id
             FROM event_push_actions_staging
             WHERE event_id = ?
         """
diff --git a/synapse/storage/databases/main/receipts.py b/synapse/storage/databases/main/receipts.py
index 03e04c215d5c..22900ddf76e9 100644
--- a/synapse/storage/databases/main/receipts.py
+++ b/synapse/storage/databases/main/receipts.py
@@ -694,6 +694,7 @@ def _insert_linearized_receipt_txn(
                 "stream_id": stream_id,
                 "event_id": event_id,
                 "data": json_encoder.encode(data),
+                "thread_id": None,
             },
             # receipts_linearized has a unique constraint on
             # (user_id, room_id, receipt_type), so no need to lock
@@ -848,6 +849,7 @@ def _insert_graph_receipt_txn(
                 "user_id": user_id,
                 "event_ids": json_encoder.encode(event_ids),
                 "data": json_encoder.encode(data),
+                "thread_id": None,
             },
         )