Merge pull request #4855 from matrix-org/rav/refactor_transaction_queue

Split TransactionQueue up

8 files changed, 865 insertions, 761 deletions

diff --git a/changelog.d/4855.misc b/changelog.d/4855.misc
new file mode 100644
index 0000000000..c4906d2f56
--- /dev/null
+++ b/changelog.d/4855.misc
@@ -0,0 +1 @@
+Refactor federation TransactionQueue.
\ No newline at end of file
diff --git a/synapse/federation/send_queue.py b/synapse/federation/send_queue.py
index bcb41da338..04d04a4457 100644
--- a/synapse/federation/send_queue.py
+++ b/synapse/federation/send_queue.py
@@ -46,7 +46,7 @@ logger = logging.getLogger(__name__)
 
 
 class FederationRemoteSendQueue(object):
-    """A drop in replacement for TransactionQueue"""
+    """A drop in replacement for FederationSender"""
 
     def __init__(self, hs):
         self.server_name = hs.hostname
@@ -154,13 +154,13 @@ class FederationRemoteSendQueue(object):
                 del self.device_messages[key]
 
     def notify_new_events(self, current_id):
-        """As per TransactionQueue"""
+        """As per FederationSender"""
         # We don't need to replicate this as it gets sent down a different
         # stream.
         pass
 
     def build_and_send_edu(self, destination, edu_type, content, key=None):
-        """As per TransactionQueue"""
+        """As per FederationSender"""
         if destination == self.server_name:
             logger.info("Not sending EDU to ourselves")
             return
@@ -184,7 +184,7 @@ class FederationRemoteSendQueue(object):
         self.notifier.on_new_replication_data()
 
     def send_read_receipt(self, receipt):
-        """As per TransactionQueue
+        """As per FederationSender
 
         Args:
             receipt (synapse.types.ReadReceipt):
@@ -193,7 +193,7 @@ class FederationRemoteSendQueue(object):
         pass
 
     def send_presence(self, states):
-        """As per TransactionQueue
+        """As per FederationSender
 
         Args:
             states (list(UserPresenceState))
@@ -210,7 +210,7 @@ class FederationRemoteSendQueue(object):
         self.notifier.on_new_replication_data()
 
     def send_device_messages(self, destination):
-        """As per TransactionQueue"""
+        """As per FederationSender"""
         pos = self._next_pos()
         self.device_messages[pos] = destination
         self.notifier.on_new_replication_data()
@@ -448,7 +448,7 @@ def process_rows_for_federation(transaction_queue, rows):
     transaction queue ready for sending to the relevant homeservers.
 
     Args:
-        transaction_queue (TransactionQueue)
+        transaction_queue (FederationSender)
         rows (list(synapse.replication.tcp.streams.FederationStreamRow))
     """
 
diff --git a/synapse/federation/sender/__init__.py b/synapse/federation/sender/__init__.py
new file mode 100644
index 0000000000..1bcc353d18
--- /dev/null
+++ b/synapse/federation/sender/__init__.py
@@ -0,0 +1,388 @@
+# -*- coding: utf-8 -*-
+# 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 logging
+
+from six import itervalues
+
+from prometheus_client import Counter
+
+from twisted.internet import defer
+
+import synapse.metrics
+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.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.util import logcontext
+from synapse.util.metrics import measure_func
+
+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",
+)
+
+
+class FederationSender(object):
+    def __init__(self, hs):
+        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._transaction_manager = TransactionManager(hs)
+
+        # 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 = {}
+
+        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._order = 1
+
+        self._is_processing = False
+        self._last_poked_id = -1
+
+        self._processing_pending_presence = False
+
+    def _get_per_destination_queue(self, destination):
+        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, current_id):
+        """This gets called when we have some new events we might want to
+        send out to other servers.
+        """
+        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,
+        )
+
+    @defer.inlineCallbacks
+    def _process_event_queue_loop(self):
+        try:
+            self._is_processing = True
+            while True:
+                last_token = yield self.store.get_federation_out_pos("events")
+                next_token, events = yield 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
+
+                @defer.inlineCallbacks
+                def handle_event(event):
+                    # 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
+
+                    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 = yield self.state.get_current_hosts_in_room(
+                            event.room_id, latest_event_ids=event.prev_event_ids(),
+                        )
+                    except Exception:
+                        logger.exception(
+                            "Failed to calculate hosts in room for event: %s",
+                            event.event_id,
+                        )
+                        return
+
+                    destinations = set(destinations)
+
+                    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)
+
+                    self._send_pdu(event, destinations)
+
+                @defer.inlineCallbacks
+                def handle_room_events(events):
+                    for event in events:
+                        yield handle_event(event)
+
+                events_by_room = {}
+                for event in events:
+                    events_by_room.setdefault(event.room_id, []).append(event)
+
+                yield logcontext.make_deferred_yieldable(defer.gatherResults(
+                    [
+                        logcontext.run_in_background(handle_room_events, evs)
+                        for evs in itervalues(events_by_room)
+                    ],
+                    consumeErrors=True
+                ))
+
+                yield self.store.update_federation_out_pos(
+                    "events", next_token
+                )
+
+                if events:
+                    now = self.clock.time_msec()
+                    ts = yield 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
+
+    def _send_pdu(self, pdu, destinations):
+        # 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.
+
+        order = self._order
+        self._order += 1
+
+        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()
+
+        for destination in destinations:
+            self._get_per_destination_queue(destination).send_pdu(pdu, order)
+
+    @defer.inlineCallbacks
+    def send_read_receipt(self, receipt):
+        """Send a RR to any other servers in the room
+
+        Args:
+            receipt (synapse.types.ReadReceipt): receipt to be sent
+        """
+        # Work out which remote servers should be poked and poke them.
+        domains = yield self.state.get_current_hosts_in_room(receipt.room_id)
+        domains = [d for d in domains if d != self.server_name]
+        if not domains:
+            return
+
+        logger.debug("Sending receipt to: %r", domains)
+
+        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)
+
+        for domain in domains:
+            self.build_and_send_edu(
+                destination=domain,
+                edu_type="m.receipt",
+                content=content,
+                key=key,
+            )
+
+    @logcontext.preserve_fn  # the caller should not yield on this
+    @defer.inlineCallbacks
+    def send_presence(self, states):
+        """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.
+
+        Args:
+            states (list(UserPresenceState))
+        """
+        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 successtion 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
+
+                yield self._process_presence_inner(list(states_map.values()))
+        except Exception:
+            logger.exception("Error sending presence states to servers")
+        finally:
+            self._processing_pending_presence = False
+
+    @measure_func("txnqueue._process_presence")
+    @defer.inlineCallbacks
+    def _process_presence_inner(self, states):
+        """Given a list of states populate self.pending_presence_by_dest and
+        poke to send a new transaction to each destination
+
+        Args:
+            states (list(UserPresenceState))
+        """
+        hosts_and_states = yield get_interested_remotes(self.store, states, self.state)
+
+        for destinations, states in hosts_and_states:
+            for destination in destinations:
+                if destination == self.server_name:
+                    continue
+                self._get_per_destination_queue(destination).send_presence(states)
+
+    def build_and_send_edu(self, destination, edu_type, content, key=None):
+        """Construct an Edu object, and queue it for sending
+
+        Args:
+            destination (str): name of server to send to
+            edu_type (str): type of EDU to send
+            content (dict): content of EDU
+            key (Any|None): clobbering key for this edu
+        """
+        if destination == self.server_name:
+            logger.info("Not sending EDU to ourselves")
+            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, key):
+        """Queue an EDU for sending
+
+        Args:
+            edu (Edu): edu to send
+            key (Any|None): clobbering key for this edu
+        """
+        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):
+        if destination == self.server_name:
+            logger.info("Not sending device update to ourselves")
+            return
+
+        self._get_per_destination_queue(destination).attempt_new_transaction()
+
+    def get_current_token(self):
+        return 0
diff --git a/synapse/federation/sender/per_destination_queue.py b/synapse/federation/sender/per_destination_queue.py
new file mode 100644
index 0000000000..385039add4
--- /dev/null
+++ b/synapse/federation/sender/per_destination_queue.py
@@ -0,0 +1,318 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014-2016 OpenMarket Ltd
+# 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 datetime
+import logging
+
+from prometheus_client import Counter
+
+from twisted.internet import defer
+
+from synapse.api.errors import (
+    FederationDeniedError,
+    HttpResponseException,
+    RequestSendFailed,
+)
+from synapse.events import EventBase
+from synapse.federation.units import Edu
+from synapse.handlers.presence import format_user_presence_state
+from synapse.metrics import sent_transactions_counter
+from synapse.metrics.background_process_metrics import run_as_background_process
+from synapse.storage import UserPresenceState
+from synapse.util.retryutils import NotRetryingDestination, get_retry_limiter
+
+logger = logging.getLogger(__name__)
+
+
+sent_edus_counter = Counter(
+    "synapse_federation_client_sent_edus",
+    "Total number of EDUs successfully sent",
+)
+
+sent_edus_by_type = Counter(
+    "synapse_federation_client_sent_edus_by_type",
+    "Number of sent EDUs successfully sent, by event type",
+    ["type"],
+)
+
+
+class PerDestinationQueue(object):
+    """
+    Manages the per-destination transmission queues.
+
+    Args:
+        hs (synapse.HomeServer):
+        transaction_sender (TransactionManager):
+        destination (str): the server_name of the destination that we are managing
+            transmission for.
+    """
+    def __init__(self, hs, transaction_manager, destination):
+        self._server_name = hs.hostname
+        self._clock = hs.get_clock()
+        self._store = hs.get_datastore()
+        self._transaction_manager = transaction_manager
+
+        self._destination = destination
+        self.transmission_loop_running = False
+
+        # a list of tuples of (pending pdu, order)
+        self._pending_pdus = []    # type: list[tuple[EventBase, int]]
+        self._pending_edus = []    # type: list[Edu]
+
+        # Pending EDUs by their "key". Keyed EDUs are EDUs that get clobbered
+        # based on their key (e.g. typing events by room_id)
+        # Map of (edu_type, key) -> Edu
+        self._pending_edus_keyed = {}   # type: dict[tuple[str, str], Edu]
+
+        # Map of user_id -> UserPresenceState of pending presence to be sent to this
+        # destination
+        self._pending_presence = {}   # type: dict[str, UserPresenceState]
+
+        # stream_id of last successfully sent to-device message.
+        # NB: may be a long or an int.
+        self._last_device_stream_id = 0
+
+        # stream_id of last successfully sent device list update.
+        self._last_device_list_stream_id = 0
+
+    def pending_pdu_count(self):
+        return len(self._pending_pdus)
+
+    def pending_edu_count(self):
+        return (
+            len(self._pending_edus)
+            + len(self._pending_presence)
+            + len(self._pending_edus_keyed)
+        )
+
+    def send_pdu(self, pdu, order):
+        """Add a PDU to the queue, and start the transmission loop if neccessary
+
+        Args:
+            pdu (EventBase): pdu to send
+            order (int):
+        """
+        self._pending_pdus.append((pdu, order))
+        self.attempt_new_transaction()
+
+    def send_presence(self, states):
+        """Add presence updates to the queue. Start the transmission loop if neccessary.
+
+        Args:
+            states (iterable[UserPresenceState]): presence to send
+        """
+        self._pending_presence.update({
+            state.user_id: state for state in states
+        })
+        self.attempt_new_transaction()
+
+    def send_keyed_edu(self, edu, key):
+        self._pending_edus_keyed[(edu.edu_type, key)] = edu
+        self.attempt_new_transaction()
+
+    def send_edu(self, edu):
+        self._pending_edus.append(edu)
+        self.attempt_new_transaction()
+
+    def attempt_new_transaction(self):
+        """Try to start a new transaction to this destination
+
+        If there is already a transaction in progress to this destination,
+        returns immediately. Otherwise kicks off the process of sending a
+        transaction in the background.
+        """
+        # list of (pending_pdu, deferred, order)
+        if self.transmission_loop_running:
+            # XXX: this can get stuck on by a never-ending
+            # request at which point pending_pdus just keeps growing.
+            # we need application-layer timeouts of some flavour of these
+            # requests
+            logger.debug(
+                "TX [%s] Transaction already in progress",
+                self._destination
+            )
+            return
+
+        logger.debug("TX [%s] Starting transaction loop", self._destination)
+
+        run_as_background_process(
+            "federation_transaction_transmission_loop",
+            self._transaction_transmission_loop,
+        )
+
+    @defer.inlineCallbacks
+    def _transaction_transmission_loop(self):
+        pending_pdus = []
+        try:
+            self.transmission_loop_running = True
+
+            # This will throw if we wouldn't retry. We do this here so we fail
+            # quickly, but we will later check this again in the http client,
+            # hence why we throw the result away.
+            yield get_retry_limiter(self._destination, self._clock, self._store)
+
+            pending_pdus = []
+            while True:
+                device_message_edus, device_stream_id, dev_list_id = (
+                    yield self._get_new_device_messages()
+                )
+
+                # BEGIN CRITICAL SECTION
+                #
+                # In order to avoid a race condition, we need to make sure that
+                # the following code (from popping the queues up to the point
+                # where we decide if we actually have any pending messages) is
+                # atomic - otherwise new PDUs or EDUs might arrive in the
+                # meantime, but not get sent because we hold the
+                # transmission_loop_running flag.
+
+                pending_pdus = self._pending_pdus
+
+                # We can only include at most 50 PDUs per transactions
+                pending_pdus, self._pending_pdus = pending_pdus[:50], pending_pdus[50:]
+
+                pending_edus = self._pending_edus
+
+                # We can only include at most 100 EDUs per transactions
+                pending_edus, self._pending_edus = pending_edus[:100], pending_edus[100:]
+
+                pending_edus.extend(
+                    self._pending_edus_keyed.values()
+                )
+
+                self._pending_edus_keyed = {}
+
+                pending_edus.extend(device_message_edus)
+
+                pending_presence = self._pending_presence
+                self._pending_presence = {}
+                if pending_presence:
+                    pending_edus.append(
+                        Edu(
+                            origin=self._server_name,
+                            destination=self._destination,
+                            edu_type="m.presence",
+                            content={
+                                "push": [
+                                    format_user_presence_state(
+                                        presence, self._clock.time_msec()
+                                    )
+                                    for presence in pending_presence.values()
+                                ]
+                            },
+                        )
+                    )
+
+                if pending_pdus:
+                    logger.debug("TX [%s] len(pending_pdus_by_dest[dest]) = %d",
+                                 self._destination, len(pending_pdus))
+
+                if not pending_pdus and not pending_edus:
+                    logger.debug("TX [%s] Nothing to send", self._destination)
+                    self._last_device_stream_id = device_stream_id
+                    return
+
+                # END CRITICAL SECTION
+
+                success = yield self._transaction_manager.send_new_transaction(
+                    self._destination, pending_pdus, pending_edus
+                )
+                if success:
+                    sent_transactions_counter.inc()
+                    sent_edus_counter.inc(len(pending_edus))
+                    for edu in pending_edus:
+                        sent_edus_by_type.labels(edu.edu_type).inc()
+                    # Remove the acknowledged device messages from the database
+                    # Only bother if we actually sent some device messages
+                    if device_message_edus:
+                        yield self._store.delete_device_msgs_for_remote(
+                            self._destination, device_stream_id
+                        )
+                        logger.info(
+                            "Marking as sent %r %r", self._destination, dev_list_id
+                        )
+                        yield self._store.mark_as_sent_devices_by_remote(
+                            self._destination, dev_list_id
+                        )
+
+                    self._last_device_stream_id = device_stream_id
+                    self._last_device_list_stream_id = dev_list_id
+                else:
+                    break
+        except NotRetryingDestination as e:
+            logger.debug(
+                "TX [%s] not ready for retry yet (next retry at %s) - "
+                "dropping transaction for now",
+                self._destination,
+                datetime.datetime.fromtimestamp(
+                    (e.retry_last_ts + e.retry_interval) / 1000.0
+                ),
+            )
+        except FederationDeniedError as e:
+            logger.info(e)
+        except HttpResponseException as e:
+            logger.warning(
+                "TX [%s] Received %d response to transaction: %s",
+                self._destination, e.code, e,
+            )
+        except RequestSendFailed as e:
+            logger.warning("TX [%s] Failed to send transaction: %s", self._destination, e)
+
+            for p, _ in pending_pdus:
+                logger.info("Failed to send event %s to %s", p.event_id,
+                            self._destination)
+        except Exception:
+            logger.exception(
+                "TX [%s] Failed to send transaction",
+                self._destination,
+            )
+            for p, _ in pending_pdus:
+                logger.info("Failed to send event %s to %s", p.event_id,
+                            self._destination)
+        finally:
+            # We want to be *very* sure we clear this after we stop processing
+            self.transmission_loop_running = False
+
+    @defer.inlineCallbacks
+    def _get_new_device_messages(self):
+        last_device_stream_id = self._last_device_stream_id
+        to_device_stream_id = self._store.get_to_device_stream_token()
+        contents, stream_id = yield self._store.get_new_device_msgs_for_remote(
+            self._destination, last_device_stream_id, to_device_stream_id
+        )
+        edus = [
+            Edu(
+                origin=self._server_name,
+                destination=self._destination,
+                edu_type="m.direct_to_device",
+                content=content,
+            )
+            for content in contents
+        ]
+
+        last_device_list = self._last_device_list_stream_id
+        now_stream_id, results = yield self._store.get_devices_by_remote(
+            self._destination, last_device_list
+        )
+        edus.extend(
+            Edu(
+                origin=self._server_name,
+                destination=self._destination,
+                edu_type="m.device_list_update",
+                content=content,
+            )
+            for content in results
+        )
+        defer.returnValue((edus, stream_id, now_stream_id))
diff --git a/synapse/federation/sender/transaction_manager.py b/synapse/federation/sender/transaction_manager.py
new file mode 100644
index 0000000000..35e6b8ff5b
--- /dev/null
+++ b/synapse/federation/sender/transaction_manager.py
@@ -0,0 +1,147 @@
+# -*- coding: utf-8 -*-
+# 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 logging
+
+from twisted.internet import defer
+
+from synapse.api.errors import HttpResponseException
+from synapse.federation.persistence import TransactionActions
+from synapse.federation.units import Transaction
+from synapse.util.metrics import measure_func
+
+logger = logging.getLogger(__name__)
+
+
+class TransactionManager(object):
+    """Helper class which handles building and sending transactions
+
+    shared between PerDestinationQueue objects
+    """
+    def __init__(self, hs):
+        self._server_name = hs.hostname
+        self.clock = hs.get_clock()   # nb must be called this for @measure_func
+        self._store = hs.get_datastore()
+        self._transaction_actions = TransactionActions(self._store)
+        self._transport_layer = hs.get_federation_transport_client()
+
+        # HACK to get unique tx id
+        self._next_txn_id = int(self.clock.time_msec())
+
+    @measure_func("_send_new_transaction")
+    @defer.inlineCallbacks
+    def send_new_transaction(self, destination, pending_pdus, pending_edus):
+
+        # Sort based on the order field
+        pending_pdus.sort(key=lambda t: t[1])
+        pdus = [x[0] for x in pending_pdus]
+        edus = pending_edus
+
+        success = True
+
+        logger.debug("TX [%s] _attempt_new_transaction", destination)
+
+        txn_id = str(self._next_txn_id)
+
+        logger.debug(
+            "TX [%s] {%s} Attempting new transaction"
+            " (pdus: %d, edus: %d)",
+            destination, txn_id,
+            len(pdus),
+            len(edus),
+        )
+
+        logger.debug("TX [%s] Persisting transaction...", destination)
+
+        transaction = Transaction.create_new(
+            origin_server_ts=int(self.clock.time_msec()),
+            transaction_id=txn_id,
+            origin=self._server_name,
+            destination=destination,
+            pdus=pdus,
+            edus=edus,
+        )
+
+        self._next_txn_id += 1
+
+        yield self._transaction_actions.prepare_to_send(transaction)
+
+        logger.debug("TX [%s] Persisted transaction", destination)
+        logger.info(
+            "TX [%s] {%s} Sending transaction [%s],"
+            " (PDUs: %d, EDUs: %d)",
+            destination, txn_id,
+            transaction.transaction_id,
+            len(pdus),
+            len(edus),
+        )
+
+        # Actually send the transaction
+
+        # FIXME (erikj): This is a bit of a hack to make the Pdu age
+        # keys work
+        def json_data_cb():
+            data = transaction.get_dict()
+            now = int(self.clock.time_msec())
+            if "pdus" in data:
+                for p in data["pdus"]:
+                    if "age_ts" in p:
+                        unsigned = p.setdefault("unsigned", {})
+                        unsigned["age"] = now - int(p["age_ts"])
+                        del p["age_ts"]
+            return data
+
+        try:
+            response = yield self._transport_layer.send_transaction(
+                transaction, json_data_cb
+            )
+            code = 200
+        except HttpResponseException as e:
+            code = e.code
+            response = e.response
+
+            if e.code in (401, 404, 429) or 500 <= e.code:
+                logger.info(
+                    "TX [%s] {%s} got %d response",
+                    destination, txn_id, code
+                )
+                raise e
+
+        logger.info(
+            "TX [%s] {%s} got %d response",
+            destination, txn_id, code
+        )
+
+        yield self._transaction_actions.delivered(
+            transaction, code, response
+        )
+
+        logger.debug("TX [%s] {%s} Marked as delivered", destination, txn_id)
+
+        if code == 200:
+            for e_id, r in response.get("pdus", {}).items():
+                if "error" in r:
+                    logger.warn(
+                        "TX [%s] {%s} Remote returned error for %s: %s",
+                        destination, txn_id, e_id, r,
+                    )
+        else:
+            for p in pdus:
+                logger.warn(
+                    "TX [%s] {%s} Failed to send event %s",
+                    destination, txn_id, p.event_id,
+                )
+            success = False
+
+        defer.returnValue(success)
diff --git a/synapse/federation/transaction_queue.py b/synapse/federation/transaction_queue.py
deleted file mode 100644
index 288cb5045c..0000000000
--- a/synapse/federation/transaction_queue.py
+++ /dev/null
@@ -1,751 +0,0 @@
-# -*- coding: utf-8 -*-
-# Copyright 2014-2016 OpenMarket 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 datetime
-import logging
-
-from six import itervalues
-
-from prometheus_client import Counter
-
-from twisted.internet import defer
-
-import synapse.metrics
-from synapse.api.errors import (
-    FederationDeniedError,
-    HttpResponseException,
-    RequestSendFailed,
-)
-from synapse.handlers.presence import format_user_presence_state, get_interested_remotes
-from synapse.metrics import (
-    LaterGauge,
-    event_processing_loop_counter,
-    event_processing_loop_room_count,
-    events_processed_counter,
-    sent_transactions_counter,
-)
-from synapse.metrics.background_process_metrics import run_as_background_process
-from synapse.util import logcontext
-from synapse.util.metrics import measure_func
-from synapse.util.retryutils import NotRetryingDestination, get_retry_limiter
-
-from .persistence import TransactionActions
-from .units import Edu, Transaction
-
-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",
-)
-
-sent_edus_counter = Counter(
-    "synapse_federation_client_sent_edus",
-    "Total number of EDUs successfully sent",
-)
-
-sent_edus_by_type = Counter(
-    "synapse_federation_client_sent_edus_by_type",
-    "Number of sent EDUs successfully sent, by event type",
-    ["type"],
-)
-
-
-class TransactionQueue(object):
-    """This class makes sure we only have one transaction in flight at
-    a time for a given destination.
-
-    It batches pending PDUs into single transactions.
-    """
-
-    def __init__(self, hs):
-        self.hs = hs
-        self.server_name = hs.hostname
-
-        self.store = hs.get_datastore()
-        self.state = hs.get_state_handler()
-        self.transaction_actions = TransactionActions(self.store)
-
-        self.transport_layer = hs.get_federation_transport_client()
-
-        self.clock = hs.get_clock()
-        self.is_mine_id = hs.is_mine_id
-
-        # Is a mapping from destinations -> deferreds. Used to keep track
-        # of which destinations have transactions in flight and when they are
-        # done
-        self.pending_transactions = {}
-
-        LaterGauge(
-            "synapse_federation_transaction_queue_pending_destinations",
-            "",
-            [],
-            lambda: len(self.pending_transactions),
-        )
-
-        # Is a mapping from destination -> list of
-        # tuple(pending pdus, deferred, order)
-        self.pending_pdus_by_dest = pdus = {}
-        # destination -> list of tuple(edu, deferred)
-        self.pending_edus_by_dest = edus = {}
-
-        # 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 = {}
-
-        # Map of destination -> user_id -> UserPresenceState of pending presence
-        # to be sent to each destinations
-        self.pending_presence_by_dest = presence = {}
-
-        # Pending EDUs by their "key". Keyed EDUs are EDUs that get clobbered
-        # based on their key (e.g. typing events by room_id)
-        # Map of destination -> (edu_type, key) -> Edu
-        self.pending_edus_keyed_by_dest = edus_keyed = {}
-
-        LaterGauge(
-            "synapse_federation_transaction_queue_pending_pdus",
-            "",
-            [],
-            lambda: sum(map(len, pdus.values())),
-        )
-        LaterGauge(
-            "synapse_federation_transaction_queue_pending_edus",
-            "",
-            [],
-            lambda: (
-                sum(map(len, edus.values()))
-                + sum(map(len, presence.values()))
-                + sum(map(len, edus_keyed.values()))
-            ),
-        )
-
-        # destination -> stream_id of last successfully sent to-device message.
-        # NB: may be a long or an int.
-        self.last_device_stream_id_by_dest = {}
-
-        # destination -> stream_id of last successfully sent device list
-        # update.
-        self.last_device_list_stream_id_by_dest = {}
-
-        # HACK to get unique tx id
-        self._next_txn_id = int(self.clock.time_msec())
-
-        self._order = 1
-
-        self._is_processing = False
-        self._last_poked_id = -1
-
-        self._processing_pending_presence = False
-
-    def notify_new_events(self, current_id):
-        """This gets called when we have some new events we might want to
-        send out to other servers.
-        """
-        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,
-        )
-
-    @defer.inlineCallbacks
-    def _process_event_queue_loop(self):
-        try:
-            self._is_processing = True
-            while True:
-                last_token = yield self.store.get_federation_out_pos("events")
-                next_token, events = yield 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
-
-                @defer.inlineCallbacks
-                def handle_event(event):
-                    # 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
-
-                    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 = yield self.state.get_current_hosts_in_room(
-                            event.room_id, latest_event_ids=event.prev_event_ids(),
-                        )
-                    except Exception:
-                        logger.exception(
-                            "Failed to calculate hosts in room for event: %s",
-                            event.event_id,
-                        )
-                        return
-
-                    destinations = set(destinations)
-
-                    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)
-
-                    self._send_pdu(event, destinations)
-
-                @defer.inlineCallbacks
-                def handle_room_events(events):
-                    for event in events:
-                        yield handle_event(event)
-
-                events_by_room = {}
-                for event in events:
-                    events_by_room.setdefault(event.room_id, []).append(event)
-
-                yield logcontext.make_deferred_yieldable(defer.gatherResults(
-                    [
-                        logcontext.run_in_background(handle_room_events, evs)
-                        for evs in itervalues(events_by_room)
-                    ],
-                    consumeErrors=True
-                ))
-
-                yield self.store.update_federation_out_pos(
-                    "events", next_token
-                )
-
-                if events:
-                    now = self.clock.time_msec()
-                    ts = yield 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
-
-    def _send_pdu(self, pdu, destinations):
-        # 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.
-
-        order = self._order
-        self._order += 1
-
-        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()
-
-        for destination in destinations:
-            self.pending_pdus_by_dest.setdefault(destination, []).append(
-                (pdu, order)
-            )
-
-            self._attempt_new_transaction(destination)
-
-    @defer.inlineCallbacks
-    def send_read_receipt(self, receipt):
-        """Send a RR to any other servers in the room
-
-        Args:
-            receipt (synapse.types.ReadReceipt): receipt to be sent
-        """
-        # Work out which remote servers should be poked and poke them.
-        domains = yield self.state.get_current_hosts_in_room(receipt.room_id)
-        domains = [d for d in domains if d != self.server_name]
-        if not domains:
-            return
-
-        logger.debug("Sending receipt to: %r", domains)
-
-        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)
-
-        for domain in domains:
-            self.build_and_send_edu(
-                destination=domain,
-                edu_type="m.receipt",
-                content=content,
-                key=key,
-            )
-
-    @logcontext.preserve_fn  # the caller should not yield on this
-    @defer.inlineCallbacks
-    def send_presence(self, states):
-        """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.
-
-        Args:
-            states (list(UserPresenceState))
-        """
-        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 successtion 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
-
-                yield self._process_presence_inner(list(states_map.values()))
-        except Exception:
-            logger.exception("Error sending presence states to servers")
-        finally:
-            self._processing_pending_presence = False
-
-    @measure_func("txnqueue._process_presence")
-    @defer.inlineCallbacks
-    def _process_presence_inner(self, states):
-        """Given a list of states populate self.pending_presence_by_dest and
-        poke to send a new transaction to each destination
-
-        Args:
-            states (list(UserPresenceState))
-        """
-        hosts_and_states = yield get_interested_remotes(self.store, states, self.state)
-
-        for destinations, states in hosts_and_states:
-            for destination in destinations:
-                if destination == self.server_name:
-                    continue
-
-                self.pending_presence_by_dest.setdefault(
-                    destination, {}
-                ).update({
-                    state.user_id: state for state in states
-                })
-
-                self._attempt_new_transaction(destination)
-
-    def build_and_send_edu(self, destination, edu_type, content, key=None):
-        """Construct an Edu object, and queue it for sending
-
-        Args:
-            destination (str): name of server to send to
-            edu_type (str): type of EDU to send
-            content (dict): content of EDU
-            key (Any|None): clobbering key for this edu
-        """
-        if destination == self.server_name:
-            logger.info("Not sending EDU to ourselves")
-            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, key):
-        """Queue an EDU for sending
-
-        Args:
-            edu (Edu): edu to send
-            key (Any|None): clobbering key for this edu
-        """
-        if key:
-            self.pending_edus_keyed_by_dest.setdefault(
-                edu.destination, {}
-            )[(edu.edu_type, key)] = edu
-        else:
-            self.pending_edus_by_dest.setdefault(edu.destination, []).append(edu)
-
-        self._attempt_new_transaction(edu.destination)
-
-    def send_device_messages(self, destination):
-        if destination == self.server_name:
-            logger.info("Not sending device update to ourselves")
-            return
-
-        self._attempt_new_transaction(destination)
-
-    def get_current_token(self):
-        return 0
-
-    def _attempt_new_transaction(self, destination):
-        """Try to start a new transaction to this destination
-
-        If there is already a transaction in progress to this destination,
-        returns immediately. Otherwise kicks off the process of sending a
-        transaction in the background.
-
-        Args:
-            destination (str):
-
-        Returns:
-            None
-        """
-        # list of (pending_pdu, deferred, order)
-        if destination in self.pending_transactions:
-            # XXX: pending_transactions can get stuck on by a never-ending
-            # request at which point pending_pdus_by_dest just keeps growing.
-            # we need application-layer timeouts of some flavour of these
-            # requests
-            logger.debug(
-                "TX [%s] Transaction already in progress",
-                destination
-            )
-            return
-
-        logger.debug("TX [%s] Starting transaction loop", destination)
-
-        run_as_background_process(
-            "federation_transaction_transmission_loop",
-            self._transaction_transmission_loop,
-            destination,
-        )
-
-    @defer.inlineCallbacks
-    def _transaction_transmission_loop(self, destination):
-        pending_pdus = []
-        try:
-            self.pending_transactions[destination] = 1
-
-            # This will throw if we wouldn't retry. We do this here so we fail
-            # quickly, but we will later check this again in the http client,
-            # hence why we throw the result away.
-            yield get_retry_limiter(destination, self.clock, self.store)
-
-            pending_pdus = []
-            while True:
-                device_message_edus, device_stream_id, dev_list_id = (
-                    yield self._get_new_device_messages(destination)
-                )
-
-                # BEGIN CRITICAL SECTION
-                #
-                # In order to avoid a race condition, we need to make sure that
-                # the following code (from popping the queues up to the point
-                # where we decide if we actually have any pending messages) is
-                # atomic - otherwise new PDUs or EDUs might arrive in the
-                # meantime, but not get sent because we hold the
-                # pending_transactions flag.
-
-                pending_pdus = self.pending_pdus_by_dest.pop(destination, [])
-
-                # We can only include at most 50 PDUs per transactions
-                pending_pdus, leftover_pdus = pending_pdus[:50], pending_pdus[50:]
-                if leftover_pdus:
-                    self.pending_pdus_by_dest[destination] = leftover_pdus
-
-                pending_edus = self.pending_edus_by_dest.pop(destination, [])
-
-                # We can only include at most 100 EDUs per transactions
-                pending_edus, leftover_edus = pending_edus[:100], pending_edus[100:]
-                if leftover_edus:
-                    self.pending_edus_by_dest[destination] = leftover_edus
-
-                pending_presence = self.pending_presence_by_dest.pop(destination, {})
-
-                pending_edus.extend(
-                    self.pending_edus_keyed_by_dest.pop(destination, {}).values()
-                )
-
-                pending_edus.extend(device_message_edus)
-                if pending_presence:
-                    pending_edus.append(
-                        Edu(
-                            origin=self.server_name,
-                            destination=destination,
-                            edu_type="m.presence",
-                            content={
-                                "push": [
-                                    format_user_presence_state(
-                                        presence, self.clock.time_msec()
-                                    )
-                                    for presence in pending_presence.values()
-                                ]
-                            },
-                        )
-                    )
-
-                if pending_pdus:
-                    logger.debug("TX [%s] len(pending_pdus_by_dest[dest]) = %d",
-                                 destination, len(pending_pdus))
-
-                if not pending_pdus and not pending_edus:
-                    logger.debug("TX [%s] Nothing to send", destination)
-                    self.last_device_stream_id_by_dest[destination] = (
-                        device_stream_id
-                    )
-                    return
-
-                # END CRITICAL SECTION
-
-                success = yield self._send_new_transaction(
-                    destination, pending_pdus, pending_edus,
-                )
-                if success:
-                    sent_transactions_counter.inc()
-                    sent_edus_counter.inc(len(pending_edus))
-                    for edu in pending_edus:
-                        sent_edus_by_type.labels(edu.edu_type).inc()
-                    # Remove the acknowledged device messages from the database
-                    # Only bother if we actually sent some device messages
-                    if device_message_edus:
-                        yield self.store.delete_device_msgs_for_remote(
-                            destination, device_stream_id
-                        )
-                        logger.info("Marking as sent %r %r", destination, dev_list_id)
-                        yield self.store.mark_as_sent_devices_by_remote(
-                            destination, dev_list_id
-                        )
-
-                    self.last_device_stream_id_by_dest[destination] = device_stream_id
-                    self.last_device_list_stream_id_by_dest[destination] = dev_list_id
-                else:
-                    break
-        except NotRetryingDestination as e:
-            logger.debug(
-                "TX [%s] not ready for retry yet (next retry at %s) - "
-                "dropping transaction for now",
-                destination,
-                datetime.datetime.fromtimestamp(
-                    (e.retry_last_ts + e.retry_interval) / 1000.0
-                ),
-            )
-        except FederationDeniedError as e:
-            logger.info(e)
-        except HttpResponseException as e:
-            logger.warning(
-                "TX [%s] Received %d response to transaction: %s",
-                destination, e.code, e,
-            )
-        except RequestSendFailed as e:
-            logger.warning("TX [%s] Failed to send transaction: %s", destination, e)
-
-            for p, _ in pending_pdus:
-                logger.info("Failed to send event %s to %s", p.event_id,
-                            destination)
-        except Exception:
-            logger.exception(
-                "TX [%s] Failed to send transaction",
-                destination,
-            )
-            for p, _ in pending_pdus:
-                logger.info("Failed to send event %s to %s", p.event_id,
-                            destination)
-        finally:
-            # We want to be *very* sure we delete this after we stop processing
-            self.pending_transactions.pop(destination, None)
-
-    @defer.inlineCallbacks
-    def _get_new_device_messages(self, destination):
-        last_device_stream_id = self.last_device_stream_id_by_dest.get(destination, 0)
-        to_device_stream_id = self.store.get_to_device_stream_token()
-        contents, stream_id = yield self.store.get_new_device_msgs_for_remote(
-            destination, last_device_stream_id, to_device_stream_id
-        )
-        edus = [
-            Edu(
-                origin=self.server_name,
-                destination=destination,
-                edu_type="m.direct_to_device",
-                content=content,
-            )
-            for content in contents
-        ]
-
-        last_device_list = self.last_device_list_stream_id_by_dest.get(destination, 0)
-        now_stream_id, results = yield self.store.get_devices_by_remote(
-            destination, last_device_list
-        )
-        edus.extend(
-            Edu(
-                origin=self.server_name,
-                destination=destination,
-                edu_type="m.device_list_update",
-                content=content,
-            )
-            for content in results
-        )
-        defer.returnValue((edus, stream_id, now_stream_id))
-
-    @measure_func("_send_new_transaction")
-    @defer.inlineCallbacks
-    def _send_new_transaction(self, destination, pending_pdus, pending_edus):
-
-        # Sort based on the order field
-        pending_pdus.sort(key=lambda t: t[1])
-        pdus = [x[0] for x in pending_pdus]
-        edus = pending_edus
-
-        success = True
-
-        logger.debug("TX [%s] _attempt_new_transaction", destination)
-
-        txn_id = str(self._next_txn_id)
-
-        logger.debug(
-            "TX [%s] {%s} Attempting new transaction"
-            " (pdus: %d, edus: %d)",
-            destination, txn_id,
-            len(pdus),
-            len(edus),
-        )
-
-        logger.debug("TX [%s] Persisting transaction...", destination)
-
-        transaction = Transaction.create_new(
-            origin_server_ts=int(self.clock.time_msec()),
-            transaction_id=txn_id,
-            origin=self.server_name,
-            destination=destination,
-            pdus=pdus,
-            edus=edus,
-        )
-
-        self._next_txn_id += 1
-
-        yield self.transaction_actions.prepare_to_send(transaction)
-
-        logger.debug("TX [%s] Persisted transaction", destination)
-        logger.info(
-            "TX [%s] {%s} Sending transaction [%s],"
-            " (PDUs: %d, EDUs: %d)",
-            destination, txn_id,
-            transaction.transaction_id,
-            len(pdus),
-            len(edus),
-        )
-
-        # Actually send the transaction
-
-        # FIXME (erikj): This is a bit of a hack to make the Pdu age
-        # keys work
-        def json_data_cb():
-            data = transaction.get_dict()
-            now = int(self.clock.time_msec())
-            if "pdus" in data:
-                for p in data["pdus"]:
-                    if "age_ts" in p:
-                        unsigned = p.setdefault("unsigned", {})
-                        unsigned["age"] = now - int(p["age_ts"])
-                        del p["age_ts"]
-            return data
-
-        try:
-            response = yield self.transport_layer.send_transaction(
-                transaction, json_data_cb
-            )
-            code = 200
-        except HttpResponseException as e:
-            code = e.code
-            response = e.response
-
-            if e.code in (401, 404, 429) or 500 <= e.code:
-                logger.info(
-                    "TX [%s] {%s} got %d response",
-                    destination, txn_id, code
-                )
-                raise e
-
-        logger.info(
-            "TX [%s] {%s} got %d response",
-            destination, txn_id, code
-        )
-
-        yield self.transaction_actions.delivered(
-            transaction, code, response
-        )
-
-        logger.debug("TX [%s] {%s} Marked as delivered", destination, txn_id)
-
-        if code == 200:
-            for e_id, r in response.get("pdus", {}).items():
-                if "error" in r:
-                    logger.warn(
-                        "TX [%s] {%s} Remote returned error for %s: %s",
-                        destination, txn_id, e_id, r,
-                    )
-        else:
-            for p in pdus:
-                logger.warn(
-                    "TX [%s] {%s} Failed to send event %s",
-                    destination, txn_id, p.event_id,
-                )
-            success = False
-
-        defer.returnValue(success)
diff --git a/synapse/server.py b/synapse/server.py
index b9549dd042..dc8f1ccb8c 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -42,7 +42,7 @@ from synapse.federation.federation_server import (
     ReplicationFederationHandlerRegistry,
 )
 from synapse.federation.send_queue import FederationRemoteSendQueue
-from synapse.federation.transaction_queue import TransactionQueue
+from synapse.federation.sender import FederationSender
 from synapse.federation.transport.client import TransportLayerClient
 from synapse.groups.attestations import GroupAttestationSigning, GroupAttestionRenewer
 from synapse.groups.groups_server import GroupsServerHandler
@@ -434,7 +434,7 @@ class HomeServer(object):
 
     def build_federation_sender(self):
         if self.should_send_federation():
-            return TransactionQueue(self)
+            return FederationSender(self)
         elif not self.config.worker_app:
             return FederationRemoteSendQueue(self)
         else:
diff --git a/synapse/server.pyi b/synapse/server.pyi
index fb8df56cd5..3ba3a967c2 100644
--- a/synapse/server.pyi
+++ b/synapse/server.pyi
@@ -1,5 +1,6 @@
 import synapse.api.auth
 import synapse.config.homeserver
+import synapse.federation.sender
 import synapse.federation.transaction_queue
 import synapse.federation.transport.client
 import synapse.handlers
@@ -62,7 +63,7 @@ class HomeServer(object):
     def get_set_password_handler(self) -> synapse.handlers.set_password.SetPasswordHandler:
         pass
 
-    def get_federation_sender(self) -> synapse.federation.transaction_queue.TransactionQueue:
+    def get_federation_sender(self) -> synapse.federation.sender.FederationSender:
         pass
 
     def get_federation_transport_client(self) -> synapse.federation.transport.client.TransportLayerClient: