diff options
Diffstat (limited to 'synapse/federation/sender/__init__.py')
| -rw-r--r-- | synapse/federation/sender/__init__.py | 115 |
1 files changed, 96 insertions, 19 deletions
diff --git a/synapse/federation/sender/__init__.py b/synapse/federation/sender/__init__.py index 1bcc353d18..1dc041752b 100644 --- a/synapse/federation/sender/__init__.py +++ b/synapse/federation/sender/__init__.py @@ -104,7 +104,26 @@ class FederationSender(object): self._processing_pending_presence = False + # map from room_id to a set of PerDestinationQueues which we believe are + # awaiting a call to flush_read_receipts_for_room. The presence of an entry + # here for a given room means that we are rate-limiting RR flushes to that room, + # and that there is a pending call to _flush_rrs_for_room in the system. + self._queues_awaiting_rr_flush_by_room = { + } # type: dict[str, set[PerDestinationQueue]] + + self._rr_txn_interval_per_room_ms = ( + 1000.0 / hs.get_config().federation_rr_transactions_per_room_per_second + ) + def _get_per_destination_queue(self, destination): + """Get or create a PerDestinationQueue for the given destination + + Args: + destination (str): server_name of remote server + + Returns: + PerDestinationQueue + """ queue = self._per_destination_queues.get(destination) if not queue: queue = PerDestinationQueue(self.hs, self._transaction_manager, destination) @@ -250,33 +269,91 @@ class FederationSender(object): Args: receipt (synapse.types.ReadReceipt): receipt to be sent """ + + # Some background on the rate-limiting going on here. + # + # It turns out that if we attempt to send out RRs as soon as we get them from + # a client, then we end up trying to do several hundred Hz of federation + # transactions. (The number of transactions scales as O(N^2) on the size of a + # room, since in a large room we have both more RRs coming in, and more servers + # to send them to.) + # + # This leads to a lot of CPU load, and we end up getting behind. The solution + # currently adopted is as follows: + # + # The first receipt in a given room is sent out immediately, at time T0. Any + # further receipts are, in theory, batched up for N seconds, where N is calculated + # based on the number of servers in the room to achieve a transaction frequency + # of around 50Hz. So, for example, if there were 100 servers in the room, then + # N would be 100 / 50Hz = 2 seconds. + # + # Then, after T+N, we flush out any receipts that have accumulated, and restart + # the timer to flush out more receipts at T+2N, etc. If no receipts accumulate, + # we stop the cycle and go back to the start. + # + # However, in practice, it is often possible to flush out receipts earlier: in + # particular, if we are sending a transaction to a given server anyway (for + # example, because we have a PDU or a RR in another room to send), then we may + # as well send out all of the pending RRs for that server. So it may be that + # by the time we get to T+N, we don't actually have any RRs left to send out. + # Nevertheless we continue to buffer up RRs for the room in question until we + # reach the point that no RRs arrive between timer ticks. + # + # For even more background, see https://github.com/matrix-org/synapse/issues/4730. + + room_id = receipt.room_id + # Work out which remote servers should be poked and poke them. - domains = yield self.state.get_current_hosts_in_room(receipt.room_id) + domains = yield self.state.get_current_hosts_in_room(room_id) domains = [d for d in domains if d != self.server_name] if not domains: return - logger.debug("Sending receipt to: %r", domains) + queues_pending_flush = self._queues_awaiting_rr_flush_by_room.get( + room_id + ) - content = { - receipt.room_id: { - receipt.receipt_type: { - receipt.user_id: { - "event_ids": receipt.event_ids, - "data": receipt.data, - }, - }, - }, - } - key = (receipt.room_id, receipt.receipt_type, receipt.user_id) + # if there is no flush yet scheduled, we will send out these receipts with + # immediate flushes, and schedule the next flush for this room. + if queues_pending_flush is not None: + logger.debug("Queuing receipt for: %r", domains) + else: + logger.debug("Sending receipt to: %r", domains) + self._schedule_rr_flush_for_room(room_id, len(domains)) for domain in domains: - self.build_and_send_edu( - destination=domain, - edu_type="m.receipt", - content=content, - key=key, - ) + queue = self._get_per_destination_queue(domain) + queue.queue_read_receipt(receipt) + + # if there is already a RR flush pending for this room, then make sure this + # destination is registered for the flush + if queues_pending_flush is not None: + queues_pending_flush.add(queue) + else: + queue.flush_read_receipts_for_room(room_id) + + def _schedule_rr_flush_for_room(self, room_id, n_domains): + # that is going to cause approximately len(domains) transactions, so now back + # off for that multiplied by RR_TXN_INTERVAL_PER_ROOM + backoff_ms = self._rr_txn_interval_per_room_ms * n_domains + + logger.debug("Scheduling RR flush in %s in %d ms", room_id, backoff_ms) + self.clock.call_later(backoff_ms, self._flush_rrs_for_room, room_id) + self._queues_awaiting_rr_flush_by_room[room_id] = set() + + def _flush_rrs_for_room(self, room_id): + queues = self._queues_awaiting_rr_flush_by_room.pop(room_id) + logger.debug("Flushing RRs in %s to %s", room_id, queues) + + if not queues: + # no more RRs arrived for this room; we are done. + return + + # schedule the next flush + self._schedule_rr_flush_for_room(room_id, len(queues)) + + for queue in queues: + queue.flush_read_receipts_for_room(room_id) @logcontext.preserve_fn # the caller should not yield on this @defer.inlineCallbacks |