Sliding Sync: Speed up getting receipts for initial rooms (#17592)

Let's only pull out the events we care about. Note that the index isn't
necessary here, as postgres is happy to scan the set of rooms for the
events.

changelog.d/17592.misc

@@ -0,0 +1 @@
+Correctly track read receipts that should be sent down in experimental sliding sync.

synapse/handlers/sliding_sync.py

@@ -3088,38 +3088,17 @@ class SlidingSyncHandler:
             # from that room but we only want to include receipts for events
             # in the timeline to avoid bloating and blowing up the sync response
             # as the number of users in the room increases. (this behavior is part of the spec)
-            initial_rooms = {
-                room_id
+            initial_rooms_and_event_ids = [
+                (room_id, event.event_id)
                 for room_id in initial_rooms
                 if room_id in actual_room_response_map
-            }
-            if initial_rooms:
-                initial_receipts = await self.store.get_linearized_receipts_for_rooms(
-                    room_ids=initial_rooms,
-                    to_key=to_token.receipt_key,
+                for event in actual_room_response_map[room_id].timeline_events
+            ]
+            if initial_rooms_and_event_ids:
+                initial_receipts = await self.store.get_linearized_receipts_for_events(
+                    room_and_event_ids=initial_rooms_and_event_ids,
                 )
-
-                for receipt in initial_receipts:
-                    relevant_event_ids = {
-                        event.event_id
-                        for event in actual_room_response_map[
-                            receipt["room_id"]
-                        ].timeline_events
-                    }
-
-                    content = {
-                        event_id: content_value
-                        for event_id, content_value in receipt["content"].items()
-                        if event_id in relevant_event_ids
-                    }
-                    if content:
-                        fetched_receipts.append(
-                            {
-                                "type": receipt["type"],
-                                "room_id": receipt["room_id"],
-                                "content": content,
-                            }
-                        )
+                fetched_receipts.extend(initial_receipts)
 
             fetched_receipts = ReceiptEventSource.filter_out_private_receipts(
                 fetched_receipts, sync_config.user.to_string()

synapse/storage/databases/main/receipts.py

@@ -43,6 +43,7 @@ from synapse.storage.database import (
     DatabasePool,
     LoggingDatabaseConnection,
     LoggingTransaction,
+    make_tuple_in_list_sql_clause,
 )
 from synapse.storage.engines._base import IsolationLevel
 from synapse.storage.util.id_generators import MultiWriterIdGenerator
@@ -481,6 +482,83 @@ class ReceiptsWorkerStore(SQLBaseStore):
         }
         return results
 
+    async def get_linearized_receipts_for_events(
+        self,
+        room_and_event_ids: Collection[Tuple[str, str]],
+    ) -> Sequence[JsonMapping]:
+        """Get all receipts for the given set of events.
+
+        Arguments:
+            room_and_event_ids: A collection of 2-tuples of room ID and
+                event IDs to fetch receipts for
+
+        Returns:
+            A list of receipts, one per room.
+        """
+
+        def get_linearized_receipts_for_events_txn(
+            txn: LoggingTransaction,
+            room_id_event_id_tuples: Collection[Tuple[str, str]],
+        ) -> List[Tuple[str, str, str, str, Optional[str], str]]:
+            clause, args = make_tuple_in_list_sql_clause(
+                self.database_engine, ("room_id", "event_id"), room_id_event_id_tuples
+            )
+
+            sql = f"""
+                SELECT room_id, receipt_type, user_id, event_id, thread_id, data
+                FROM receipts_linearized
+                WHERE {clause}
+            """
+
+            txn.execute(sql, args)
+
+            return txn.fetchall()
+
+        # room_id -> event_id -> receipt_type -> user_id -> receipt data
+        room_to_content: Dict[str, Dict[str, Dict[str, Dict[str, JsonMapping]]]] = {}
+        for batch in batch_iter(room_and_event_ids, 1000):
+            batch_results = await self.db_pool.runInteraction(
+                "get_linearized_receipts_for_events",
+                get_linearized_receipts_for_events_txn,
+                batch,
+            )
+
+            for (
+                room_id,
+                receipt_type,
+                user_id,
+                event_id,
+                thread_id,
+                data,
+            ) in batch_results:
+                content = room_to_content.setdefault(room_id, {})
+                user_receipts = content.setdefault(event_id, {}).setdefault(
+                    receipt_type, {}
+                )
+
+                receipt_data = db_to_json(data)
+                if thread_id is not None:
+                    receipt_data["thread_id"] = thread_id
+
+                # MSC4102: always replace threaded receipts with unthreaded ones
+                # if there is a clash. Specifically:
+                # - if there is no existing receipt, great, set the data.
+                # - if there is an existing receipt, is it threaded (thread_id
+                #    present)? YES: replace if this receipt has no thread id.
+                # NO: do not replace. This means we will drop some receipts, but
+                # MSC4102 is designed to drop semantically meaningless receipts,
+                # so this is okay. Previously, we would drop meaningful data!
+                if user_id in user_receipts:
+                    if "thread_id" in user_receipts[user_id] and not thread_id:
+                        user_receipts[user_id] = receipt_data
+                else:
+                    user_receipts[user_id] = receipt_data
+
+        return [
+            {"type": EduTypes.RECEIPT, "room_id": room_id, "content": content}
+            for room_id, content in room_to_content.items()
+        ]
+
     @cached(
         num_args=2,
     )
@@ -996,6 +1074,12 @@ class ReceiptsBackgroundUpdateStore(SQLBaseStore):
             self.RECEIPTS_GRAPH_UNIQUE_INDEX_UPDATE_NAME,
             self._background_receipts_graph_unique_index,
         )
+        self.db_pool.updates.register_background_index_update(
+            update_name="receipts_room_id_event_id_index",
+            index_name="receipts_linearized_event_id",
+            table="receipts_linearized",
+            columns=("room_id", "event_id"),
+        )
 
     async def _populate_receipt_event_stream_ordering(
         self, progress: JsonDict, batch_size: int

synapse/storage/schema/main/delta/86/02_receipts_event_id_index.sql

@@ -0,0 +1,15 @@
+--
+-- This file is licensed under the Affero General Public License (AGPL) version 3.
+--
+-- Copyright (C) 2024 New Vector, Ltd
+--
+-- This program is free software: you can redistribute it and/or modify
+-- it under the terms of the GNU Affero General Public License as
+-- published by the Free Software Foundation, either version 3 of the
+-- License, or (at your option) any later version.
+--
+-- See the GNU Affero General Public License for more details:
+-- <https://www.gnu.org/licenses/agpl-3.0.html>.
+
+INSERT INTO background_updates (ordering, update_name, progress_json) VALUES
+    (8602, 'receipts_room_id_event_id_index', '{}');