Speed up get_unread_event_push_actions_by_room (#13005)

Fixes #11887 hopefully.

The core change here is that `event_push_summary` now holds a summary of counts up until a much more recent point, meaning that the range of rows we need to count in `event_push_actions` is much smaller.

This needs two major changes:
1. When we get a receipt we need to recalculate `event_push_summary` rather than just delete it
2. The logic for deleting `event_push_actions` is now divorced from calculating `event_push_summary`.

In future it would be good to calculate `event_push_summary` while we persist a new event (it should just be a case of adding one to the relevant rows in `event_push_summary`), as that will further simplify the get counts logic and remove the need for us to periodically update `event_push_summary` in a background job.

tests/storage/test_event_push_actions.py

@@ -51,10 +51,16 @@ class EventPushActionsStoreTestCase(HomeserverTestCase):
         room_id = "!foo:example.com"
         user_id = "@user1235:example.com"
 
+        last_read_stream_ordering = [0]
+
         def _assert_counts(noitf_count, highlight_count):
             counts = self.get_success(
                 self.store.db_pool.runInteraction(
-                    "", self.store._get_unread_counts_by_pos_txn, room_id, user_id, 0
+                    "",
+                    self.store._get_unread_counts_by_pos_txn,
+                    room_id,
+                    user_id,
+                    last_read_stream_ordering[0],
                 )
             )
             self.assertEqual(
@@ -98,6 +104,7 @@ class EventPushActionsStoreTestCase(HomeserverTestCase):
             )
 
         def _mark_read(stream, depth):
+            last_read_stream_ordering[0] = stream
             self.get_success(
                 self.store.db_pool.runInteraction(
                     "",
@@ -144,8 +151,19 @@ class EventPushActionsStoreTestCase(HomeserverTestCase):
         _assert_counts(1, 1)
         _rotate(9)
         _assert_counts(1, 1)
-        _rotate(10)
-        _assert_counts(1, 1)
+
+        # Check that adding another notification and rotating after highlight
+        # works.
+        _inject_actions(10, PlAIN_NOTIF)
+        _rotate(11)
+        _assert_counts(2, 1)
+
+        # Check that sending read receipts at different points results in the
+        # right counts.
+        _mark_read(8, 8)
+        _assert_counts(1, 0)
+        _mark_read(10, 10)
+        _assert_counts(0, 0)
 
     def test_find_first_stream_ordering_after_ts(self):
         def add_event(so, ts):