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Batch up outgoing read-receipts to reduce federation traffic. (#4890) 

Rate-limit outgoing read-receipts as per #4730.
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Richard van der Hoff 2019-03-20 16:02:25 +00:00 committed by GitHub
parent 11f2125885
commit a902d13180
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7 changed files with 308 additions and 22 deletions
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1
changelog.d/4890.feature Normal file
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@ -0,0 +1 @@
Batch up outgoing read-receipts to reduce federation traffic.

8
docs/sample_config.yaml
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@ -438,6 +438,14 @@ log_config: "CONFDIR/SERVERNAME.log.config"
#
#federation_rc_concurrent: 3
# Target outgoing federation transaction frequency for sending read-receipts,
# per-room.
#
# If we end up trying to send out more read-receipts, they will get buffered up
# into fewer transactions.
#
#federation_rr_transactions_per_room_per_second: 50
# Directory where uploaded images and attachments are stored.

12
synapse/config/ratelimiting.py
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@ -42,6 +42,10 @@ class RatelimitConfig(Config):
self.federation_rc_reject_limit = config.get("federation_rc_reject_limit", 50)
self.federation_rc_concurrent = config.get("federation_rc_concurrent", 3)
self.federation_rr_transactions_per_room_per_second = config.get(
"federation_rr_transactions_per_room_per_second", 50,
)
def default_config(self, **kwargs):
return """\
## Ratelimiting ##
@ -111,4 +115,12 @@ class RatelimitConfig(Config):
# single server
#
#federation_rc_concurrent: 3
# Target outgoing federation transaction frequency for sending read-receipts,
# per-room.
#
# If we end up trying to send out more read-receipts, they will get buffered up
# into fewer transactions.
#
#federation_rr_transactions_per_room_per_second: 50
"""

115
synapse/federation/sender/__init__.py
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@ -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

64
synapse/federation/sender/per_destination_queue.py
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@ -80,6 +80,10 @@ class PerDestinationQueue(object):
# destination
self._pending_presence = {} # type: dict[str, UserPresenceState]
# room_id -> receipt_type -> user_id -> receipt_dict
self._pending_rrs = {}
self._rrs_pending_flush = False
# stream_id of last successfully sent to-device message.
# NB: may be a long or an int.
self._last_device_stream_id = 0
@ -87,6 +91,9 @@ class PerDestinationQueue(object):
# stream_id of last successfully sent device list update.
self._last_device_list_stream_id = 0
def __str__(self):
return "PerDestinationQueue[%s]" % self._destination
def pending_pdu_count(self):
return len(self._pending_pdus)
@ -118,6 +125,30 @@ class PerDestinationQueue(object):
})
self.attempt_new_transaction()
def queue_read_receipt(self, receipt):
"""Add a RR to the list to be sent. Doesn't start the transmission loop yet
(see flush_read_receipts_for_room)
Args:
receipt (synapse.api.receipt_info.ReceiptInfo): receipt to be queued
"""
self._pending_rrs.setdefault(
receipt.room_id, {},
).setdefault(
receipt.receipt_type, {}
)[receipt.user_id] = {
"event_ids": receipt.event_ids,
"data": receipt.data,
}
def flush_read_receipts_for_room(self, room_id):
# if we don't have any read-receipts for this room, it may be that we've already
# sent them out, so we don't need to flush.
if room_id not in self._pending_rrs:
return
self._rrs_pending_flush = True
self.attempt_new_transaction()
def send_keyed_edu(self, edu, key):
self._pending_edus_keyed[(edu.edu_type, key)] = edu
self.attempt_new_transaction()
@ -183,10 +214,12 @@ class PerDestinationQueue(object):
# 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
pending_edus = []
pending_edus.extend(self._get_rr_edus(force_flush=False))
# 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._pop_pending_edus(100 - len(pending_edus)))
pending_edus.extend(
self._pending_edus_keyed.values()
@ -224,6 +257,11 @@ class PerDestinationQueue(object):
self._last_device_stream_id = device_stream_id
return
# if we've decided to send a transaction anyway, and we have room, we
# may as well send any pending RRs
if len(pending_edus) < 100:
pending_edus.extend(self._get_rr_edus(force_flush=True))
# END CRITICAL SECTION
success = yield self._transaction_manager.send_new_transaction(
@ -285,6 +323,28 @@ class PerDestinationQueue(object):
# We want to be *very* sure we clear this after we stop processing
self.transmission_loop_running = False
def _get_rr_edus(self, force_flush):
if not self._pending_rrs:
return
if not force_flush and not self._rrs_pending_flush:
# not yet time for this lot
return
edu = Edu(
origin=self._server_name,
destination=self._destination,
edu_type="m.receipt",
content=self._pending_rrs,
)
self._pending_rrs = {}
self._rrs_pending_flush = False
yield edu
def _pop_pending_edus(self, limit):
pending_edus = self._pending_edus
pending_edus, self._pending_edus = pending_edus[:limit], pending_edus[limit:]
return pending_edus
@defer.inlineCallbacks
def _get_new_device_messages(self):
last_device_stream_id = self._last_device_stream_id

2
synapse/handlers/receipts.py
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@ -118,7 +118,7 @@ class ReceiptsHandler(BaseHandler):
if not is_new:
return
self.federation.send_read_receipt(receipt)
yield self.federation.send_read_receipt(receipt)
@defer.inlineCallbacks
def get_receipts_for_room(self, room_id, to_key):

128
tests/federation/test_federation_sender.py Normal file
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@ -0,0 +1,128 @@
# -*- 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.
from mock import Mock
from twisted.internet import defer
from synapse.types import ReadReceipt
from tests.unittest import HomeserverTestCase
class FederationSenderTestCases(HomeserverTestCase):
def make_homeserver(self, reactor, clock):
return super(FederationSenderTestCases, self).setup_test_homeserver(
state_handler=Mock(spec=["get_current_hosts_in_room"]),
federation_transport_client=Mock(spec=["send_transaction"]),
)
def test_send_receipts(self):
mock_state_handler = self.hs.get_state_handler()
mock_state_handler.get_current_hosts_in_room.return_value = ["test", "host2"]
mock_send_transaction = self.hs.get_federation_transport_client().send_transaction
mock_send_transaction.return_value = defer.succeed({})
sender = self.hs.get_federation_sender()
receipt = ReadReceipt("room_id", "m.read", "user_id", ["event_id"], {"ts": 1234})
self.successResultOf(sender.send_read_receipt(receipt))
self.pump()
# expect a call to send_transaction
mock_send_transaction.assert_called_once()
json_cb = mock_send_transaction.call_args[0][1]
data = json_cb()
self.assertEqual(data['edus'], [
{
'edu_type': 'm.receipt',
'content': {
'room_id': {
'm.read': {
'user_id': {
'event_ids': ['event_id'],
'data': {'ts': 1234},
},
},
},
},
},
])
def test_send_receipts_with_backoff(self):
"""Send two receipts in quick succession; the second should be flushed, but
only after 20ms"""
mock_state_handler = self.hs.get_state_handler()
mock_state_handler.get_current_hosts_in_room.return_value = ["test", "host2"]
mock_send_transaction = self.hs.get_federation_transport_client().send_transaction
mock_send_transaction.return_value = defer.succeed({})
sender = self.hs.get_federation_sender()
receipt = ReadReceipt("room_id", "m.read", "user_id", ["event_id"], {"ts": 1234})
self.successResultOf(sender.send_read_receipt(receipt))
self.pump()
# expect a call to send_transaction
mock_send_transaction.assert_called_once()
json_cb = mock_send_transaction.call_args[0][1]
data = json_cb()
self.assertEqual(data['edus'], [
{
'edu_type': 'm.receipt',
'content': {
'room_id': {
'm.read': {
'user_id': {
'event_ids': ['event_id'],
'data': {'ts': 1234},
},
},
},
},
},
])
mock_send_transaction.reset_mock()
# send the second RR
receipt = ReadReceipt("room_id", "m.read", "user_id", ["other_id"], {"ts": 1234})
self.successResultOf(sender.send_read_receipt(receipt))
self.pump()
mock_send_transaction.assert_not_called()
self.reactor.advance(19)
mock_send_transaction.assert_not_called()
self.reactor.advance(10)
mock_send_transaction.assert_called_once()
json_cb = mock_send_transaction.call_args[0][1]
data = json_cb()
self.assertEqual(data['edus'], [
{
'edu_type': 'm.receipt',
'content': {
'room_id': {
'm.read': {
'user_id': {
'event_ids': ['other_id'],
'data': {'ts': 1234},
},
},
},
},
},
])