Improve appservice handler to send only the most recent read receipts when no stream_id is stored. (#8744)

* Make this line debug (it's noisy)

* Don't include from_key for presence if we are at 0

* Limit read receipts for all rooms to 100

* changelog.d/8744.bugfix

* Allow from_key to be None

* Update 8744.bugfix

* The from_key is superflous

* Update comment

3 files changed, 9 insertions, 3 deletions

diff --git a/synapse/handlers/appservice.py b/synapse/handlers/appservice.py
index 9fc8444228..5c6458eb52 100644
--- a/synapse/handlers/appservice.py
+++ b/synapse/handlers/appservice.py
@@ -226,7 +226,7 @@ class ApplicationServicesHandler:
         new_token: Optional[int],
         users: Collection[Union[str, UserID]],
     ):
-        logger.info("Checking interested services for %s" % (stream_key))
+        logger.debug("Checking interested services for %s" % (stream_key))
         with Measure(self.clock, "notify_interested_services_ephemeral"):
             for service in services:
                 # Only handle typing if we have the latest token
diff --git a/synapse/handlers/receipts.py b/synapse/handlers/receipts.py
index c242c409cf..153cbae7b9 100644
--- a/synapse/handlers/receipts.py
+++ b/synapse/handlers/receipts.py
@@ -158,7 +158,8 @@ class ReceiptEventSource:
         if from_key == to_key:
             return [], to_key
 
-        # We first need to fetch all new receipts
+        # Fetch all read receipts for all rooms, up to a limit of 100. This is ordered
+        # by most recent.
         rooms_to_events = await self.store.get_linearized_receipts_for_all_rooms(
             from_key=from_key, to_key=to_key
         )
diff --git a/synapse/storage/databases/main/receipts.py b/synapse/storage/databases/main/receipts.py
index ca7917c989..1e7949a323 100644
--- a/synapse/storage/databases/main/receipts.py
+++ b/synapse/storage/databases/main/receipts.py
@@ -278,7 +278,8 @@ class ReceiptsWorkerStore(SQLBaseStore, metaclass=abc.ABCMeta):
     async def get_linearized_receipts_for_all_rooms(
         self, to_key: int, from_key: Optional[int] = None
     ) -> Dict[str, JsonDict]:
-        """Get receipts for all rooms between two stream_ids.
+        """Get receipts for all rooms between two stream_ids, up
+        to a limit of the latest 100 read receipts.
 
         Args:
             to_key: Max stream id to fetch receipts upto.
@@ -294,12 +295,16 @@ class ReceiptsWorkerStore(SQLBaseStore, metaclass=abc.ABCMeta):
                 sql = """
                     SELECT * FROM receipts_linearized WHERE
                     stream_id > ? AND stream_id <= ?
+                    ORDER BY stream_id DESC
+                    LIMIT 100
                 """
                 txn.execute(sql, [from_key, to_key])
             else:
                 sql = """
                     SELECT * FROM receipts_linearized WHERE
                     stream_id <= ?
+                    ORDER BY stream_id DESC
+                    LIMIT 100
                 """
 
                 txn.execute(sql, [to_key])