diff --git a/synapse/replication/tcp/handler.py b/synapse/replication/tcp/handler.py
index 6f7054d5af..0e8a38fd80 100644
--- a/synapse/replication/tcp/handler.py
+++ b/synapse/replication/tcp/handler.py
@@ -99,7 +99,8 @@ 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]
LaterGauge(
diff --git a/synapse/replication/tcp/redis.py b/synapse/replication/tcp/redis.py
index 617e860f95..61dbf4ddbe 100644
--- a/synapse/replication/tcp/redis.py
+++ b/synapse/replication/tcp/redis.py
@@ -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.
"""
@@ -61,12 +67,22 @@ class RedisSubscriber(txredisapi.SubscriberProtocol, AbstractConnection):
outbound_redis_connection = None # type: txredisapi.RedisProtocol
def connectionMade(self):
- logger.info("Connected to redis instance")
- self.subscribe(self.stream_name)
- self.send_command(ReplicateCommand())
-
+ logger.info("Connected to redis")
+ 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.
"""
@@ -119,7 +135,7 @@ class RedisSubscriber(txredisapi.SubscriberProtocol, AbstractConnection):
logger.warning("Unhandled command: %r", cmd)
def connectionLost(self, reason):
- logger.info("Lost connection to redis instance")
+ logger.info("Lost connection to redis")
self.handler.lost_connection(self)
def send_command(self, cmd: Command):
@@ -128,6 +144,10 @@ class RedisSubscriber(txredisapi.SubscriberProtocol, AbstractConnection):
Args:
cmd (Command)
"""
+ run_as_background_process("send-cmd", self._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)
@@ -138,15 +158,9 @@ 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):
|
