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Merge pull request #7427 from matrix-org/rav/fix_dropped_messages

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Fix lost events on replication reconnection
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Richard van der Hoff 2020-05-06 10:54:25 +01:00 committed by GitHub
commit c255b0ffdc
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3 changed files with 71 additions and 35 deletions
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1
changelog.d/7427.feature Normal file
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@ -0,0 +1 @@
Add support for running replication over Redis when using workers.

53
synapse/replication/tcp/handler.py
View file

@ -81,9 +81,6 @@ class ReplicationCommandHandler:
self._instance_id = hs.get_instance_id()
self._instance_name = hs.get_instance_name()
# Set of streams that we've caught up with.
self._streams_connected = set() # type: Set[str]
self._streams = {
stream.NAME: stream(hs) for stream in STREAMS_MAP.values()
} # type: Dict[str, Stream]
@ -99,9 +96,13 @@ class ReplicationCommandHandler:
# The factory used to create connections.
self._factory = None # type: Optional[ReconnectingClientFactory]
# The currently connected connections.
# The currently connected connections. (The list of places we need to send
# outgoing replication commands to.)
self._connections = [] # type: List[AbstractConnection]
# For each connection, the incoming streams that are coming from that connection
self._streams_by_connection = {} # type: Dict[AbstractConnection, Set[str]]
LaterGauge(
"synapse_replication_tcp_resource_total_connections",
"",
@ -257,9 +258,11 @@ class ReplicationCommandHandler:
# 2. so we don't race with getting a POSITION command and fetching
# missing RDATA.
with await self._position_linearizer.queue(cmd.stream_name):
if stream_name not in self._streams_connected:
# If the stream isn't marked as connected then we haven't seen a
# `POSITION` command yet, and so we may have missed some rows.
# make sure that we've processed a POSITION for this stream *on this
# connection*. (A POSITION on another connection is no good, as there
# is no guarantee that we have seen all the intermediate updates.)
sbc = self._streams_by_connection.get(conn)
if not sbc or stream_name not in sbc:
# Let's drop the row for now, on the assumption we'll receive a
# `POSITION` soon and we'll catch up correctly then.
logger.debug(
@ -302,21 +305,25 @@ class ReplicationCommandHandler:
# Ignore POSITION that are just our own echoes
return
stream = self._streams.get(cmd.stream_name)
logger.info("Handling '%s %s'", cmd.NAME, cmd.to_line())
stream_name = cmd.stream_name
stream = self._streams.get(stream_name)
if not stream:
logger.error("Got POSITION for unknown stream: %s", cmd.stream_name)
logger.error("Got POSITION for unknown stream: %s", stream_name)
return
# We protect catching up with a linearizer in case the replication
# connection reconnects under us.
with await self._position_linearizer.queue(cmd.stream_name):
with await self._position_linearizer.queue(stream_name):
# We're about to go and catch up with the stream, so remove from set
# of connected streams.
self._streams_connected.discard(cmd.stream_name)
for streams in self._streams_by_connection.values():
streams.discard(stream_name)
# We clear the pending batches for the stream as the fetching of the
# missing updates below will fetch all rows in the batch.
self._pending_batches.pop(cmd.stream_name, [])
self._pending_batches.pop(stream_name, [])
# Find where we previously streamed up to.
current_token = stream.current_token()
@ -326,6 +333,12 @@ class ReplicationCommandHandler:
# between then and now.
missing_updates = cmd.token != current_token
while missing_updates:
logger.info(
"Fetching replication rows for '%s' between %i and %i",
stream_name,
current_token,
cmd.token,
)
(
updates,
current_token,
@ -341,16 +354,18 @@ class ReplicationCommandHandler:
for token, rows in _batch_updates(updates):
await self.on_rdata(
cmd.stream_name,
stream_name,
cmd.instance_name,
token,
[stream.parse_row(row) for row in rows],
)
# We've now caught up to position sent to us, notify handler.
await self._replication_data_handler.on_position(cmd.stream_name, cmd.token)
logger.info("Caught up with stream '%s' to %i", stream_name, cmd.token)
self._streams_connected.add(cmd.stream_name)
# We've now caught up to position sent to us, notify handler.
await self._replication_data_handler.on_position(stream_name, cmd.token)
self._streams_by_connection.setdefault(conn, set()).add(stream_name)
async def on_REMOTE_SERVER_UP(
self, conn: AbstractConnection, cmd: RemoteServerUpCommand
@ -408,6 +423,12 @@ class ReplicationCommandHandler:
def lost_connection(self, connection: AbstractConnection):
"""Called when a connection is closed/lost.
"""
# we no longer need _streams_by_connection for this connection.
streams = self._streams_by_connection.pop(connection, None)
if streams:
logger.info(
"Lost replication connection; streams now disconnected: %s", streams
)
try:
self._connections.remove(connection)
except ValueError:

52
synapse/replication/tcp/redis.py
View file

@ -18,7 +18,7 @@ from typing import TYPE_CHECKING
import txredisapi
from synapse.logging.context import PreserveLoggingContext
from synapse.logging.context import make_deferred_yieldable
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.replication.tcp.commands import (
Command,
@ -41,8 +41,14 @@ logger = logging.getLogger(__name__)
class RedisSubscriber(txredisapi.SubscriberProtocol, AbstractConnection):
"""Connection to redis subscribed to replication stream.
Parses incoming messages from redis into replication commands, and passes
them to `ReplicationCommandHandler`
This class fulfils two functions:
(a) it implements the twisted Protocol API, where it handles the SUBSCRIBEd redis
connection, parsing *incoming* messages into replication commands, and passing them
to `ReplicationCommandHandler`
(b) it implements the AbstractConnection API, where it sends *outgoing* commands
onto outbound_redis_connection.
Due to the vagaries of `txredisapi` we don't want to have a custom
constructor, so instead we expect the defined attributes below to be set
@ -50,8 +56,8 @@ class RedisSubscriber(txredisapi.SubscriberProtocol, AbstractConnection):
Attributes:
handler: The command handler to handle incoming commands.
stream_name: The *redis* stream name to subscribe to (not anything to
do with Synapse replication streams).
stream_name: The *redis* stream name to subscribe to and publish from
(not anything to do with Synapse replication streams).
outbound_redis_connection: The connection to redis to use to send
commands.
"""
@ -61,13 +67,23 @@ class RedisSubscriber(txredisapi.SubscriberProtocol, AbstractConnection):
outbound_redis_connection = None # type: txredisapi.RedisProtocol
def connectionMade(self):
logger.info("Connected to redis")
super().connectionMade()
logger.info("Connected to redis instance")
self.subscribe(self.stream_name)
self.send_command(ReplicateCommand())
run_as_background_process("subscribe-replication", self._send_subscribe)
self.handler.new_connection(self)
async def _send_subscribe(self):
# it's important to make sure that we only send the REPLICATE command once we
# have successfully subscribed to the stream - otherwise we might miss the
# POSITION response sent back by the other end.
logger.info("Sending redis SUBSCRIBE for %s", self.stream_name)
await make_deferred_yieldable(self.subscribe(self.stream_name))
logger.info(
"Successfully subscribed to redis stream, sending REPLICATE command"
)
await self._async_send_command(ReplicateCommand())
logger.info("REPLICATE successfully sent")
def messageReceived(self, pattern: str, channel: str, message: str):
"""Received a message from redis.
"""
@ -120,8 +136,8 @@ class RedisSubscriber(txredisapi.SubscriberProtocol, AbstractConnection):
logger.warning("Unhandled command: %r", cmd)
def connectionLost(self, reason):
logger.info("Lost connection to redis")
super().connectionLost(reason)
logger.info("Lost connection to redis instance")
self.handler.lost_connection(self)
def send_command(self, cmd: Command):
@ -130,6 +146,10 @@ class RedisSubscriber(txredisapi.SubscriberProtocol, AbstractConnection):
Args:
cmd (Command)
"""
run_as_background_process("send-cmd", self._async_send_command, cmd)
async def _async_send_command(self, cmd: Command):
"""Encode a replication command and send it over our outbound connection"""
string = "%s %s" % (cmd.NAME, cmd.to_line())
if "\n" in string:
raise Exception("Unexpected newline in command: %r", string)
@ -140,15 +160,9 @@ class RedisSubscriber(txredisapi.SubscriberProtocol, AbstractConnection):
# remote instances.
tcp_outbound_commands_counter.labels(cmd.NAME, "redis").inc()
async def _send():
with PreserveLoggingContext():
# Note that we use the other connection as we can't send
# commands using the subscription connection.
await self.outbound_redis_connection.publish(
self.stream_name, encoded_string
)
run_as_background_process("send-cmd", _send)
await make_deferred_yieldable(
self.outbound_redis_connection.publish(self.stream_name, encoded_string)
)
class RedisDirectTcpReplicationClientFactory(txredisapi.SubscriberFactory):