From a0cd8ae8cbe14d2821cbe8fd6b011c4ddc729344 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Fri, 4 Jun 2021 10:47:58 +0100
Subject: [PATCH] Don't try and backfill the same room in parallel. (#10116)
If backfilling is slow then the client may time out and retry, causing
Synapse to start a new `/backfill` before the existing backfill has
finished, duplicating work.
---
changelog.d/10116.bugfix | 1 +
synapse/handlers/federation.py | 8 ++++++++
2 files changed, 9 insertions(+)
create mode 100644 changelog.d/10116.bugfix
diff --git a/changelog.d/10116.bugfix b/changelog.d/10116.bugfix
new file mode 100644
index 0000000000..90ef707559
--- /dev/null
+++ b/changelog.d/10116.bugfix
@@ -0,0 +1 @@
+Fix bug where the server would attempt to fetch the same history in the room from a remote server multiple times in parallel.
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index f3f97db2fa..b802822baa 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -178,6 +178,8 @@ class FederationHandler(BaseHandler):
self.room_queues = {} # type: Dict[str, List[Tuple[EventBase, str]]]
self._room_pdu_linearizer = Linearizer("fed_room_pdu")
+ self._room_backfill = Linearizer("room_backfill")
+
self.third_party_event_rules = hs.get_third_party_event_rules()
self._ephemeral_messages_enabled = hs.config.enable_ephemeral_messages
@@ -1041,6 +1043,12 @@ class FederationHandler(BaseHandler):
return. This is used as part of the heuristic to decide if we
should back paginate.
"""
+ with (await self._room_backfill.queue(room_id)):
+ return await self._maybe_backfill_inner(room_id, current_depth, limit)
+
+ async def _maybe_backfill_inner(
+ self, room_id: str, current_depth: int, limit: int
+ ) -> bool:
extremities = await self.store.get_oldest_events_with_depth_in_room(room_id)
if not extremities:
--
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