# Copyright 2019 New Vector Ltd # # 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. import abc import logging from typing import TYPE_CHECKING, Dict, Hashable, Iterable, List, Optional, Set, Tuple from prometheus_client import Counter from twisted.internet import defer import synapse.metrics from synapse.api.presence import UserPresenceState from synapse.events import EventBase from synapse.federation.sender.per_destination_queue import PerDestinationQueue from synapse.federation.sender.transaction_manager import TransactionManager from synapse.federation.units import Edu from synapse.handlers.presence import get_interested_remotes from synapse.logging.context import ( make_deferred_yieldable, preserve_fn, run_in_background, ) from synapse.metrics import ( LaterGauge, event_processing_loop_counter, event_processing_loop_room_count, events_processed_counter, ) from synapse.metrics.background_process_metrics import run_as_background_process from synapse.types import JsonDict, ReadReceipt, RoomStreamToken from synapse.util.metrics import Measure, measure_func if TYPE_CHECKING: from synapse.events.presence_router import PresenceRouter from synapse.server import HomeServer logger = logging.getLogger(__name__) sent_pdus_destination_dist_count = Counter( "synapse_federation_client_sent_pdu_destinations:count", "Number of PDUs queued for sending to one or more destinations", ) sent_pdus_destination_dist_total = Counter( "synapse_federation_client_sent_pdu_destinations:total", "Total number of PDUs queued for sending across all destinations", ) # Time (in s) after Synapse's startup that we will begin to wake up destinations # that have catch-up outstanding. CATCH_UP_STARTUP_DELAY_SEC = 15 # Time (in s) to wait in between waking up each destination, i.e. one destination # will be woken up every seconds after Synapse's startup until we have woken # every destination has outstanding catch-up. CATCH_UP_STARTUP_INTERVAL_SEC = 5 class AbstractFederationSender(metaclass=abc.ABCMeta): @abc.abstractmethod def notify_new_events(self, max_token: RoomStreamToken) -> None: """This gets called when we have some new events we might want to send out to other servers. """ raise NotImplementedError() @abc.abstractmethod async def send_read_receipt(self, receipt: ReadReceipt) -> None: """Send a RR to any other servers in the room Args: receipt: receipt to be sent """ raise NotImplementedError() @abc.abstractmethod def send_presence(self, states: List[UserPresenceState]) -> None: """Send the new presence states to the appropriate destinations. This actually queues up the presence states ready for sending and triggers a background task to process them and send out the transactions. """ raise NotImplementedError() @abc.abstractmethod def send_presence_to_destinations( self, states: Iterable[UserPresenceState], destinations: Iterable[str] ) -> None: """Send the given presence states to the given destinations. Args: destinations: """ raise NotImplementedError() @abc.abstractmethod def build_and_send_edu( self, destination: str, edu_type: str, content: JsonDict, key: Optional[Hashable] = None, ) -> None: """Construct an Edu object, and queue it for sending Args: destination: name of server to send to edu_type: type of EDU to send content: content of EDU key: clobbering key for this edu """ raise NotImplementedError() @abc.abstractmethod def send_device_messages(self, destination: str) -> None: raise NotImplementedError() @abc.abstractmethod def wake_destination(self, destination: str) -> None: """Called when we want to retry sending transactions to a remote. This is mainly useful if the remote server has been down and we think it might have come back. """ raise NotImplementedError() @abc.abstractmethod def get_current_token(self) -> int: raise NotImplementedError() @abc.abstractmethod def federation_ack(self, instance_name: str, token: int) -> None: raise NotImplementedError() @abc.abstractmethod async def get_replication_rows( self, instance_name: str, from_token: int, to_token: int, target_row_count: int ) -> Tuple[List[Tuple[int, Tuple]], int, bool]: raise NotImplementedError() class FederationSender(AbstractFederationSender): def __init__(self, hs: "HomeServer"): self.hs = hs self.server_name = hs.hostname self.store = hs.get_datastore() self.state = hs.get_state_handler() self.clock = hs.get_clock() self.is_mine_id = hs.is_mine_id self._presence_router = None # type: Optional[PresenceRouter] self._transaction_manager = TransactionManager(hs) self._instance_name = hs.get_instance_name() self._federation_shard_config = hs.config.worker.federation_shard_config # map from destination to PerDestinationQueue self._per_destination_queues = {} # type: Dict[str, PerDestinationQueue] LaterGauge( "synapse_federation_transaction_queue_pending_destinations", "", [], lambda: sum( 1 for d in self._per_destination_queues.values() if d.transmission_loop_running ), ) # Map of user_id -> UserPresenceState for all the pending presence # to be sent out by user_id. Entries here get processed and put in # pending_presence_by_dest self.pending_presence = {} # type: Dict[str, UserPresenceState] LaterGauge( "synapse_federation_transaction_queue_pending_pdus", "", [], lambda: sum( d.pending_pdu_count() for d in self._per_destination_queues.values() ), ) LaterGauge( "synapse_federation_transaction_queue_pending_edus", "", [], lambda: sum( d.pending_edu_count() for d in self._per_destination_queues.values() ), ) self._is_processing = False self._last_poked_id = -1 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.config.federation_rr_transactions_per_room_per_second ) # wake up destinations that have outstanding PDUs to be caught up self._catchup_after_startup_timer = self.clock.call_later( CATCH_UP_STARTUP_DELAY_SEC, run_as_background_process, "wake_destinations_needing_catchup", self._wake_destinations_needing_catchup, ) self._external_cache = hs.get_external_cache() def _get_per_destination_queue(self, destination: str) -> PerDestinationQueue: """Get or create a PerDestinationQueue for the given destination Args: destination: server_name of remote server """ queue = self._per_destination_queues.get(destination) if not queue: queue = PerDestinationQueue(self.hs, self._transaction_manager, destination) self._per_destination_queues[destination] = queue return queue def notify_new_events(self, max_token: RoomStreamToken) -> None: """This gets called when we have some new events we might want to send out to other servers. """ # We just use the minimum stream ordering and ignore the vector clock # component. This is safe to do as long as we *always* ignore the vector # clock components. current_id = max_token.stream self._last_poked_id = max(current_id, self._last_poked_id) if self._is_processing: return # fire off a processing loop in the background run_as_background_process( "process_event_queue_for_federation", self._process_event_queue_loop ) async def _process_event_queue_loop(self) -> None: try: self._is_processing = True while True: last_token = await self.store.get_federation_out_pos("events") next_token, events = await self.store.get_all_new_events_stream( last_token, self._last_poked_id, limit=100 ) logger.debug("Handling %s -> %s", last_token, next_token) if not events and next_token >= self._last_poked_id: break async def handle_event(event: EventBase) -> None: # Only send events for this server. send_on_behalf_of = event.internal_metadata.get_send_on_behalf_of() is_mine = self.is_mine_id(event.sender) if not is_mine and send_on_behalf_of is None: return if not event.internal_metadata.should_proactively_send(): return destinations = None # type: Optional[Set[str]] if not event.prev_event_ids(): # If there are no prev event IDs then the state is empty # and so no remote servers in the room destinations = set() else: # We check the external cache for the destinations, which is # stored per state group. sg = await self._external_cache.get( "event_to_prev_state_group", event.event_id ) if sg: destinations = await self._external_cache.get( "get_joined_hosts", str(sg) ) if destinations is None: try: # Get the state from before the event. # We need to make sure that this is the state from before # the event and not from after it. # Otherwise if the last member on a server in a room is # banned then it won't receive the event because it won't # be in the room after the ban. destinations = await self.state.get_hosts_in_room_at_events( event.room_id, event_ids=event.prev_event_ids() ) except Exception: logger.exception( "Failed to calculate hosts in room for event: %s", event.event_id, ) return destinations = { d for d in destinations if self._federation_shard_config.should_handle( self._instance_name, d ) } if send_on_behalf_of is not None: # If we are sending the event on behalf of another server # then it already has the event and there is no reason to # send the event to it. destinations.discard(send_on_behalf_of) logger.debug("Sending %s to %r", event, destinations) if destinations: await self._send_pdu(event, destinations) now = self.clock.time_msec() ts = await self.store.get_received_ts(event.event_id) synapse.metrics.event_processing_lag_by_event.labels( "federation_sender" ).observe((now - ts) / 1000) async def handle_room_events(events: Iterable[EventBase]) -> None: with Measure(self.clock, "handle_room_events"): for event in events: await handle_event(event) events_by_room = {} # type: Dict[str, List[EventBase]] for event in events: events_by_room.setdefault(event.room_id, []).append(event) await make_deferred_yieldable( defer.gatherResults( [ run_in_background(handle_room_events, evs) for evs in events_by_room.values() ], consumeErrors=True, ) ) await self.store.update_federation_out_pos("events", next_token) if events: now = self.clock.time_msec() ts = await self.store.get_received_ts(events[-1].event_id) synapse.metrics.event_processing_lag.labels( "federation_sender" ).set(now - ts) synapse.metrics.event_processing_last_ts.labels( "federation_sender" ).set(ts) events_processed_counter.inc(len(events)) event_processing_loop_room_count.labels("federation_sender").inc( len(events_by_room) ) event_processing_loop_counter.labels("federation_sender").inc() synapse.metrics.event_processing_positions.labels( "federation_sender" ).set(next_token) finally: self._is_processing = False async def _send_pdu(self, pdu: EventBase, destinations: Iterable[str]) -> None: # We loop through all destinations to see whether we already have # a transaction in progress. If we do, stick it in the pending_pdus # table and we'll get back to it later. destinations = set(destinations) destinations.discard(self.server_name) logger.debug("Sending to: %s", str(destinations)) if not destinations: return sent_pdus_destination_dist_total.inc(len(destinations)) sent_pdus_destination_dist_count.inc() assert pdu.internal_metadata.stream_ordering # track the fact that we have a PDU for these destinations, # to allow us to perform catch-up later on if the remote is unreachable # for a while. await self.store.store_destination_rooms_entries( destinations, pdu.room_id, pdu.internal_metadata.stream_ordering, ) for destination in destinations: self._get_per_destination_queue(destination).send_pdu(pdu) async def send_read_receipt(self, receipt: ReadReceipt) -> None: """Send a RR to any other servers in the room Args: receipt: 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_set = await self.state.get_current_hosts_in_room(room_id) domains = [ d for d in domains_set if d != self.server_name and self._federation_shard_config.should_handle(self._instance_name, d) ] if not domains: return queues_pending_flush = self._queues_awaiting_rr_flush_by_room.get(room_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: 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: str, n_domains: int) -> None: # 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: str) -> None: 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) @preserve_fn # the caller should not yield on this async def send_presence(self, states: List[UserPresenceState]) -> None: """Send the new presence states to the appropriate destinations. This actually queues up the presence states ready for sending and triggers a background task to process them and send out the transactions. """ if not self.hs.config.use_presence: # No-op if presence is disabled. return # First we queue up the new presence by user ID, so multiple presence # updates in quick succession are correctly handled. # We only want to send presence for our own users, so lets always just # filter here just in case. self.pending_presence.update( {state.user_id: state for state in states if self.is_mine_id(state.user_id)} ) # We then handle the new pending presence in batches, first figuring # out the destinations we need to send each state to and then poking it # to attempt a new transaction. We linearize this so that we don't # accidentally mess up the ordering and send multiple presence updates # in the wrong order if self._processing_pending_presence: return self._processing_pending_presence = True try: while True: states_map = self.pending_presence self.pending_presence = {} if not states_map: break await self._process_presence_inner(list(states_map.values())) except Exception: logger.exception("Error sending presence states to servers") finally: self._processing_pending_presence = False def send_presence_to_destinations( self, states: Iterable[UserPresenceState], destinations: Iterable[str] ) -> None: """Send the given presence states to the given destinations. destinations (list[str]) """ if not states or not self.hs.config.use_presence: # No-op if presence is disabled. return for destination in destinations: if destination == self.server_name: continue if not self._federation_shard_config.should_handle( self._instance_name, destination ): continue self._get_per_destination_queue(destination).send_presence(states) @measure_func("txnqueue._process_presence") async def _process_presence_inner(self, states: List[UserPresenceState]) -> None: """Given a list of states populate self.pending_presence_by_dest and poke to send a new transaction to each destination """ # We pull the presence router here instead of __init__ # to prevent a dependency cycle: # # AuthHandler -> Notifier -> FederationSender # -> PresenceRouter -> ModuleApi -> AuthHandler if self._presence_router is None: self._presence_router = self.hs.get_presence_router() assert self._presence_router is not None hosts_and_states = await get_interested_remotes( self.store, self._presence_router, states, self.state, ) for destinations, states in hosts_and_states: for destination in destinations: if destination == self.server_name: continue if not self._federation_shard_config.should_handle( self._instance_name, destination ): continue self._get_per_destination_queue(destination).send_presence(states) def build_and_send_edu( self, destination: str, edu_type: str, content: JsonDict, key: Optional[Hashable] = None, ) -> None: """Construct an Edu object, and queue it for sending Args: destination: name of server to send to edu_type: type of EDU to send content: content of EDU key: clobbering key for this edu """ if destination == self.server_name: logger.info("Not sending EDU to ourselves") return if not self._federation_shard_config.should_handle( self._instance_name, destination ): return edu = Edu( origin=self.server_name, destination=destination, edu_type=edu_type, content=content, ) self.send_edu(edu, key) def send_edu(self, edu: Edu, key: Optional[Hashable]) -> None: """Queue an EDU for sending Args: edu: edu to send key: clobbering key for this edu """ if not self._federation_shard_config.should_handle( self._instance_name, edu.destination ): return queue = self._get_per_destination_queue(edu.destination) if key: queue.send_keyed_edu(edu, key) else: queue.send_edu(edu) def send_device_messages(self, destination: str) -> None: if destination == self.server_name: logger.warning("Not sending device update to ourselves") return if not self._federation_shard_config.should_handle( self._instance_name, destination ): return self._get_per_destination_queue(destination).attempt_new_transaction() def wake_destination(self, destination: str) -> None: """Called when we want to retry sending transactions to a remote. This is mainly useful if the remote server has been down and we think it might have come back. """ if destination == self.server_name: logger.warning("Not waking up ourselves") return if not self._federation_shard_config.should_handle( self._instance_name, destination ): return self._get_per_destination_queue(destination).attempt_new_transaction() @staticmethod def get_current_token() -> int: # Dummy implementation for case where federation sender isn't offloaded # to a worker. return 0 def federation_ack(self, instance_name: str, token: int) -> None: # It is not expected that this gets called on FederationSender. raise NotImplementedError() @staticmethod async def get_replication_rows( instance_name: str, from_token: int, to_token: int, target_row_count: int ) -> Tuple[List[Tuple[int, Tuple]], int, bool]: # Dummy implementation for case where federation sender isn't offloaded # to a worker. return [], 0, False async def _wake_destinations_needing_catchup(self) -> None: """ Wakes up destinations that need catch-up and are not currently being backed off from. In order to reduce load spikes, adds a delay between each destination. """ last_processed = None # type: Optional[str] while True: destinations_to_wake = ( await self.store.get_catch_up_outstanding_destinations(last_processed) ) if not destinations_to_wake: # finished waking all destinations! self._catchup_after_startup_timer = None break last_processed = destinations_to_wake[-1] destinations_to_wake = [ d for d in destinations_to_wake if self._federation_shard_config.should_handle(self._instance_name, d) ] for destination in destinations_to_wake: logger.info( "Destination %s has outstanding catch-up, waking up.", last_processed, ) self.wake_destination(destination) await self.clock.sleep(CATCH_UP_STARTUP_INTERVAL_SEC)