Remove support for aggregating reactions (#15172)

It turns out that no clients rely on server-side aggregation of `m.annotation`
relationships: it's just not very useful as currently implemented.

It's also non-trivial to calculate.

I want to remove it from MSC2677, so to keep the implementation in line, let's
remove it here.

6 files changed, 1 insertions, 227 deletions

diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index ebf8c7ed83..eaa6cad4af 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -516,11 +516,6 @@ class EventClientSerializer:
         # being serialized.
         serialized_aggregations = {}
 
-        if event_aggregations.annotations:
-            serialized_aggregations[
-                RelationTypes.ANNOTATION
-            ] = event_aggregations.annotations
-
         if event_aggregations.references:
             serialized_aggregations[
                 RelationTypes.REFERENCE
diff --git a/synapse/handlers/relations.py b/synapse/handlers/relations.py
index 0fb15391e0..553053b694 100644
--- a/synapse/handlers/relations.py
+++ b/synapse/handlers/relations.py
@@ -60,13 +60,12 @@ class BundledAggregations:
     Some values require additional processing during serialization.
     """
 
-    annotations: Optional[JsonDict] = None
     references: Optional[JsonDict] = None
     replace: Optional[EventBase] = None
     thread: Optional[_ThreadAggregation] = None
 
     def __bool__(self) -> bool:
-        return bool(self.annotations or self.references or self.replace or self.thread)
+        return bool(self.references or self.replace or self.thread)
 
 
 class RelationsHandler:
@@ -227,67 +226,6 @@ class RelationsHandler:
                     e.msg,
                 )
 
-    async def get_annotations_for_events(
-        self, event_ids: Collection[str], ignored_users: FrozenSet[str] = frozenset()
-    ) -> Dict[str, List[JsonDict]]:
-        """Get a list of annotations to the given events, grouped by event type and
-        aggregation key, sorted by count.
-
-        This is used e.g. to get the what and how many reactions have happened
-        on an event.
-
-        Args:
-            event_ids: Fetch events that relate to these event IDs.
-            ignored_users: The users ignored by the requesting user.
-
-        Returns:
-            A map of event IDs to a list of groups of annotations that match.
-            Each entry is a dict with `type`, `key` and `count` fields.
-        """
-        # Get the base results for all users.
-        full_results = await self._main_store.get_aggregation_groups_for_events(
-            event_ids
-        )
-
-        # Avoid additional logic if there are no ignored users.
-        if not ignored_users:
-            return {
-                event_id: results
-                for event_id, results in full_results.items()
-                if results
-            }
-
-        # Then subtract off the results for any ignored users.
-        ignored_results = await self._main_store.get_aggregation_groups_for_users(
-            [event_id for event_id, results in full_results.items() if results],
-            ignored_users,
-        )
-
-        filtered_results = {}
-        for event_id, results in full_results.items():
-            # If no annotations, skip.
-            if not results:
-                continue
-
-            # If there are not ignored results for this event, copy verbatim.
-            if event_id not in ignored_results:
-                filtered_results[event_id] = results
-                continue
-
-            # Otherwise, subtract out the ignored results.
-            event_ignored_results = ignored_results[event_id]
-            for result in results:
-                key = (result["type"], result["key"])
-                if key in event_ignored_results:
-                    # Ensure to not modify the cache.
-                    result = result.copy()
-                    result["count"] -= event_ignored_results[key]
-                    if result["count"] <= 0:
-                        continue
-                filtered_results.setdefault(event_id, []).append(result)
-
-        return filtered_results
-
     async def get_references_for_events(
         self, event_ids: Collection[str], ignored_users: FrozenSet[str] = frozenset()
     ) -> Dict[str, List[_RelatedEvent]]:
@@ -531,17 +469,6 @@ class RelationsHandler:
                 # (as that is what makes it part of the thread).
                 relations_by_id[latest_thread_event.event_id] = RelationTypes.THREAD
 
-        async def _fetch_annotations() -> None:
-            """Fetch any annotations (ie, reactions) to bundle with this event."""
-            annotations_by_event_id = await self.get_annotations_for_events(
-                events_by_id.keys(), ignored_users=ignored_users
-            )
-            for event_id, annotations in annotations_by_event_id.items():
-                if annotations:
-                    results.setdefault(event_id, BundledAggregations()).annotations = {
-                        "chunk": annotations
-                    }
-
         async def _fetch_references() -> None:
             """Fetch any references to bundle with this event."""
             references_by_event_id = await self.get_references_for_events(
@@ -575,7 +502,6 @@ class RelationsHandler:
         await make_deferred_yieldable(
             gather_results(
                 (
-                    run_in_background(_fetch_annotations),
                     run_in_background(_fetch_references),
                     run_in_background(_fetch_edits),
                 )
diff --git a/synapse/storage/databases/main/cache.py b/synapse/storage/databases/main/cache.py
index 5b66431691..096dec7f87 100644
--- a/synapse/storage/databases/main/cache.py
+++ b/synapse/storage/databases/main/cache.py
@@ -266,9 +266,6 @@ class CacheInvalidationWorkerStore(SQLBaseStore):
         if relates_to:
             self._attempt_to_invalidate_cache("get_relations_for_event", (relates_to,))
             self._attempt_to_invalidate_cache("get_references_for_event", (relates_to,))
-            self._attempt_to_invalidate_cache(
-                "get_aggregation_groups_for_event", (relates_to,)
-            )
             self._attempt_to_invalidate_cache("get_applicable_edit", (relates_to,))
             self._attempt_to_invalidate_cache("get_thread_summary", (relates_to,))
             self._attempt_to_invalidate_cache("get_thread_participated", (relates_to,))
diff --git a/synapse/storage/databases/main/events.py b/synapse/storage/databases/main/events.py
index 73b8aea16c..a8a4ed4436 100644
--- a/synapse/storage/databases/main/events.py
+++ b/synapse/storage/databases/main/events.py
@@ -2024,10 +2024,6 @@ class PersistEventsStore:
         self.store._invalidate_cache_and_stream(
             txn, self.store.get_relations_for_event, (redacted_relates_to,)
         )
-        if rel_type == RelationTypes.ANNOTATION:
-            self.store._invalidate_cache_and_stream(
-                txn, self.store.get_aggregation_groups_for_event, (redacted_relates_to,)
-            )
         if rel_type == RelationTypes.REFERENCE:
             self.store._invalidate_cache_and_stream(
                 txn, self.store.get_references_for_event, (redacted_relates_to,)
diff --git a/synapse/storage/databases/main/events_bg_updates.py b/synapse/storage/databases/main/events_bg_updates.py
index 0a275e6ce6..daef3685b0 100644
--- a/synapse/storage/databases/main/events_bg_updates.py
+++ b/synapse/storage/databases/main/events_bg_updates.py
@@ -1220,9 +1220,6 @@ class EventsBackgroundUpdatesStore(SQLBaseStore):
                         txn, self.get_relations_for_event, cache_tuple  # type: ignore[attr-defined]
                     )
                     self._invalidate_cache_and_stream(  # type: ignore[attr-defined]
-                        txn, self.get_aggregation_groups_for_event, cache_tuple  # type: ignore[attr-defined]
-                    )
-                    self._invalidate_cache_and_stream(  # type: ignore[attr-defined]
                         txn, self.get_thread_summary, cache_tuple  # type: ignore[attr-defined]
                     )
 
diff --git a/synapse/storage/databases/main/relations.py b/synapse/storage/databases/main/relations.py
index fa3266c081..bc3a83919c 100644
--- a/synapse/storage/databases/main/relations.py
+++ b/synapse/storage/databases/main/relations.py
@@ -398,143 +398,6 @@ class RelationsWorkerStore(SQLBaseStore):
         return result is not None
 
     @cached()
-    async def get_aggregation_groups_for_event(
-        self, event_id: str
-    ) -> Sequence[JsonDict]:
-        raise NotImplementedError()
-
-    @cachedList(
-        cached_method_name="get_aggregation_groups_for_event", list_name="event_ids"
-    )
-    async def get_aggregation_groups_for_events(
-        self, event_ids: Collection[str]
-    ) -> Mapping[str, Optional[List[JsonDict]]]:
-        """Get a list of annotations on the given events, grouped by event type and
-        aggregation key, sorted by count.
-
-        This is used e.g. to get the what and how many reactions have happend
-        on an event.
-
-        Args:
-            event_ids: Fetch events that relate to these event IDs.
-
-        Returns:
-            A map of event IDs to a list of groups of annotations that match.
-            Each entry is a dict with `type`, `key` and `count` fields.
-        """
-        # The number of entries to return per event ID.
-        limit = 5
-
-        clause, args = make_in_list_sql_clause(
-            self.database_engine, "relates_to_id", event_ids
-        )
-        args.append(RelationTypes.ANNOTATION)
-
-        sql = f"""
-            SELECT
-                relates_to_id,
-                annotation.type,
-                aggregation_key,
-                COUNT(DISTINCT annotation.sender)
-            FROM events AS annotation
-            INNER JOIN event_relations USING (event_id)
-            INNER JOIN events AS parent ON
-                parent.event_id = relates_to_id
-                AND parent.room_id = annotation.room_id
-            WHERE
-                {clause}
-                AND relation_type = ?
-            GROUP BY relates_to_id, annotation.type, aggregation_key
-            ORDER BY relates_to_id, COUNT(*) DESC
-        """
-
-        def _get_aggregation_groups_for_events_txn(
-            txn: LoggingTransaction,
-        ) -> Mapping[str, List[JsonDict]]:
-            txn.execute(sql, args)
-
-            result: Dict[str, List[JsonDict]] = {}
-            for event_id, type, key, count in cast(
-                List[Tuple[str, str, str, int]], txn
-            ):
-                event_results = result.setdefault(event_id, [])
-
-                # Limit the number of results per event ID.
-                if len(event_results) == limit:
-                    continue
-
-                event_results.append({"type": type, "key": key, "count": count})
-
-            return result
-
-        return await self.db_pool.runInteraction(
-            "get_aggregation_groups_for_events", _get_aggregation_groups_for_events_txn
-        )
-
-    async def get_aggregation_groups_for_users(
-        self, event_ids: Collection[str], users: FrozenSet[str]
-    ) -> Dict[str, Dict[Tuple[str, str], int]]:
-        """Fetch the partial aggregations for an event for specific users.
-
-        This is used, in conjunction with get_aggregation_groups_for_event, to
-        remove information from the results for ignored users.
-
-        Args:
-            event_ids: Fetch events that relate to these event IDs.
-            users: The users to fetch information for.
-
-        Returns:
-            A map of event ID to a map of (event type, aggregation key) to a
-            count of users.
-        """
-
-        if not users:
-            return {}
-
-        events_sql, args = make_in_list_sql_clause(
-            self.database_engine, "relates_to_id", event_ids
-        )
-
-        users_sql, users_args = make_in_list_sql_clause(
-            self.database_engine, "annotation.sender", users
-        )
-        args.extend(users_args)
-        args.append(RelationTypes.ANNOTATION)
-
-        sql = f"""
-            SELECT
-                relates_to_id,
-                annotation.type,
-                aggregation_key,
-                COUNT(DISTINCT annotation.sender)
-            FROM events AS annotation
-            INNER JOIN event_relations USING (event_id)
-            INNER JOIN events AS parent ON
-                parent.event_id = relates_to_id
-                AND parent.room_id = annotation.room_id
-            WHERE {events_sql} AND {users_sql} AND relation_type = ?
-            GROUP BY relates_to_id, annotation.type, aggregation_key
-            ORDER BY relates_to_id, COUNT(*) DESC
-        """
-
-        def _get_aggregation_groups_for_users_txn(
-            txn: LoggingTransaction,
-        ) -> Dict[str, Dict[Tuple[str, str], int]]:
-            txn.execute(sql, args)
-
-            result: Dict[str, Dict[Tuple[str, str], int]] = {}
-            for event_id, type, key, count in cast(
-                List[Tuple[str, str, str, int]], txn
-            ):
-                result.setdefault(event_id, {})[(type, key)] = count
-
-            return result
-
-        return await self.db_pool.runInteraction(
-            "get_aggregation_groups_for_users", _get_aggregation_groups_for_users_txn
-        )
-
-    @cached()
     async def get_references_for_event(self, event_id: str) -> List[JsonDict]:
         raise NotImplementedError()