diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index 218df884b0..ff00f0b302 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -97,10 +97,16 @@ class FederationServer(FederationBase):
self.state = hs.get_state_handler()
self.device_handler = hs.get_device_handler()
+ self._federation_ratelimiter = hs.get_federation_ratelimiter()
self._server_linearizer = Linearizer("fed_server")
self._transaction_linearizer = Linearizer("fed_txn_handler")
+ # We cache results for transaction with the same ID
+ self._transaction_resp_cache = ResponseCache(
+ hs, "fed_txn_handler", timeout_ms=30000
+ )
+
self.transaction_actions = TransactionActions(self.store)
self.registry = hs.get_federation_registry()
@@ -135,22 +141,44 @@ class FederationServer(FederationBase):
request_time = self._clock.time_msec()
transaction = Transaction(**transaction_data)
+ transaction_id = transaction.transaction_id # type: ignore
- if not transaction.transaction_id: # type: ignore
+ if not transaction_id:
raise Exception("Transaction missing transaction_id")
- logger.debug("[%s] Got transaction", transaction.transaction_id) # type: ignore
+ logger.debug("[%s] Got transaction", transaction_id)
- # use a linearizer to ensure that we don't process the same transaction
- # multiple times in parallel.
- with (
- await self._transaction_linearizer.queue(
- (origin, transaction.transaction_id) # type: ignore
- )
- ):
- result = await self._handle_incoming_transaction(
- origin, transaction, request_time
- )
+ # We wrap in a ResponseCache so that we de-duplicate retried
+ # transactions.
+ return await self._transaction_resp_cache.wrap(
+ (origin, transaction_id),
+ self._on_incoming_transaction_inner,
+ origin,
+ transaction,
+ request_time,
+ )
+
+ async def _on_incoming_transaction_inner(
+ self, origin: str, transaction: Transaction, request_time: int
+ ) -> Tuple[int, Dict[str, Any]]:
+ # Use a linearizer to ensure that transactions from a remote are
+ # processed in order.
+ with await self._transaction_linearizer.queue(origin):
+ # We rate limit here *after* we've queued up the incoming requests,
+ # so that we don't fill up the ratelimiter with blocked requests.
+ #
+ # This is important as the ratelimiter allows N concurrent requests
+ # at a time, and only starts ratelimiting if there are more requests
+ # than that being processed at a time. If we queued up requests in
+ # the linearizer/response cache *after* the ratelimiting then those
+ # queued up requests would count as part of the allowed limit of N
+ # concurrent requests.
+ with self._federation_ratelimiter.ratelimit(origin) as d:
+ await d
+
+ result = await self._handle_incoming_transaction(
+ origin, transaction, request_time
+ )
return result
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