Make historical messages available to federated servers

Part of MSC2716: https://github.com/matrix-org/matrix-doc/pull/2716

Follow-up to https://github.com/matrix-org/synapse/pull/9247

synapse/handlers/federation.py

@@ -1052,6 +1052,7 @@ class FederationHandler(BaseHandler):
         with (await self._room_backfill.queue(room_id)):
             return await self._maybe_backfill_inner(room_id, current_depth, limit)
 
+    # Todo
     async def _maybe_backfill_inner(
         self, room_id: str, current_depth: int, limit: int
     ) -> bool:

synapse/storage/databases/main/event_federation.py

@@ -663,6 +663,8 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore, SQLBas
             " ON g.event_id = e.event_id"
             " INNER JOIN event_backward_extremities as b"
             " ON g.prev_event_id = b.event_id"
+            " INNER JOIN insertion_event_extremeties as i"
+            " ON g.event_id = i.insertion_prev_event_id"
             " WHERE b.room_id = ? AND g.is_state is ?"
             " GROUP BY b.event_id"
         )

synapse/storage/databases/main/events.py

@@ -1504,6 +1504,8 @@ class PersistEventsStore:
 
             self._handle_event_relations(txn, event)
 
+            self._handle_marker_event(txn, event)
+
             # Store the labels for this event.
             labels = event.content.get(EventContentFields.LABELS)
             if labels:
@@ -1756,6 +1758,39 @@ class PersistEventsStore:
         if rel_type == RelationTypes.REPLACE:
             txn.call_after(self.store.get_applicable_edit.invalidate, (parent_id,))
 
+    def _handle_marker_event(self, txn, event):
+        """Handles inserting insertion extremeties during peristence of marker events
+
+        Args:
+            txn
+            event (EventBase)
+        """
+
+        if event.type != EventTypes.MSC2716_MARKER:
+            # Not a marker event
+            return
+
+        insertion_event_id = event.content.get(
+            EventContentFields.MSC2716_MARKER_INSERTION
+        )
+        insertion_prev_event_ids = event.content.get(
+            EventContentFields.MSC2716_MARKER_INSERTION_PREV_EVENTS
+        )
+        if not insertion_event_id or not insertion_prev_event_ids:
+            # Invalid marker event
+            return
+
+        for prev_event_id in insertion_prev_event_ids:
+            self.db_pool.simple_insert_txn(
+                txn,
+                table="insertion_event_extremeties",
+                values={
+                    "insertion_event_id": insertion_event_id,
+                    "room_id": event.room_id,
+                    "insertion_prev_event_id": prev_event_id,
+                },
+            )
+
     def _handle_redaction(self, txn, redacted_event_id):
         """Handles receiving a redaction and checking whether we need to remove
         any redacted relations from the database.

synapse/storage/schema/main/delta/59/14insertion_event_lookups.sql

@@ -0,0 +1,40 @@
+/* Copyright 2021 The Matrix.org Foundation C.I.C
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+-- Add a table that keeps track of "insertion" events back in the history
+-- when we get a "marker" event over the "live" timeline. When navigating the DAG
+-- and we hit an event which matches `insertion_prev_event_id`, it should backfill 
+-- the "insertion" event and start navigating from there.
+
+
+CREATE TABLE IF NOT EXISTS insertion_event_extremeties(
+    insertion_event_id TEXT NOT NULL,
+    room_id TEXT NOT NULL,
+    insertion_prev_event_id TEXT NOT NULL,
+    UNIQUE (insertion_event_id, room_id, room_id, insertion_prev_event_id)
+);
+
+CREATE INDEX IF NOT EXISTS insertion_event_extremeties_insertion_room_id ON insertion_event_extremeties(room_id);
+CREATE INDEX IF NOT EXISTS insertion_event_extremeties_insertion_event_id ON insertion_event_extremeties(insertion_event_id);
+CREATE INDEX IF NOT EXISTS insertion_event_extremeties_insertion_prev_event_id ON insertion_event_extremeties(insertion_prev_event_id);
+
+CREATE TABLE IF NOT EXISTS chunk_connections(
+    event_id TEXT NOT NULL,
+    room_id TEXT NOT NULL,
+    chunk_id TEXT NOT NULL,
+    UNIQUE (event_id, room_id)
+);
+
+CREATE INDEX IF NOT EXISTS chunk_connections_insertion_chunk_id ON chunk_connections(chunk_id);