Remove usage of "conn_id" for presence. (#7128)

* Remove `conn_id` usage for UserSyncCommand.

Each tcp replication connection is assigned a "conn_id", which is used
to give an ID to a remotely connected worker. In a redis world, there
will no longer be a one to one mapping between connection and instance,
so instead we need to replace such usages with an ID generated by the
remote instances and included in the replicaiton commands.

This really only effects UserSyncCommand.

* Add CLEAR_USER_SYNCS command that is sent on shutdown.

This should help with the case where a synchrotron gets restarted
gracefully, rather than rely on 5 minute timeout.

4 files changed, 50 insertions, 18 deletions

diff --git a/synapse/replication/tcp/client.py b/synapse/replication/tcp/client.py
index 7e7ad0f798..e86d9805f1 100644
--- a/synapse/replication/tcp/client.py
+++ b/synapse/replication/tcp/client.py
@@ -189,10 +189,12 @@ class ReplicationClientHandler(AbstractReplicationClientHandler):
         """
         self.send_command(FederationAckCommand(token))
 
-    def send_user_sync(self, user_id, is_syncing, last_sync_ms):
+    def send_user_sync(self, instance_id, user_id, is_syncing, last_sync_ms):
         """Poke the master that a user has started/stopped syncing.
         """
-        self.send_command(UserSyncCommand(user_id, is_syncing, last_sync_ms))
+        self.send_command(
+            UserSyncCommand(instance_id, user_id, is_syncing, last_sync_ms)
+        )
 
     def send_remove_pusher(self, app_id, push_key, user_id):
         """Poke the master to remove a pusher for a user
diff --git a/synapse/replication/tcp/commands.py b/synapse/replication/tcp/commands.py
index 5a6b734094..e4eec643f7 100644
--- a/synapse/replication/tcp/commands.py
+++ b/synapse/replication/tcp/commands.py
@@ -207,30 +207,32 @@ class UserSyncCommand(Command):
 
     Format::
 
-        USER_SYNC <user_id> <state> <last_sync_ms>
+        USER_SYNC <instance_id> <user_id> <state> <last_sync_ms>
 
     Where <state> is either "start" or "stop"
     """
 
     NAME = "USER_SYNC"
 
-    def __init__(self, user_id, is_syncing, last_sync_ms):
+    def __init__(self, instance_id, user_id, is_syncing, last_sync_ms):
+        self.instance_id = instance_id
         self.user_id = user_id
         self.is_syncing = is_syncing
         self.last_sync_ms = last_sync_ms
 
     @classmethod
     def from_line(cls, line):
-        user_id, state, last_sync_ms = line.split(" ", 2)
+        instance_id, user_id, state, last_sync_ms = line.split(" ", 3)
 
         if state not in ("start", "end"):
             raise Exception("Invalid USER_SYNC state %r" % (state,))
 
-        return cls(user_id, state == "start", int(last_sync_ms))
+        return cls(instance_id, user_id, state == "start", int(last_sync_ms))
 
     def to_line(self):
         return " ".join(
             (
+                self.instance_id,
                 self.user_id,
                 "start" if self.is_syncing else "end",
                 str(self.last_sync_ms),
@@ -238,6 +240,30 @@ class UserSyncCommand(Command):
         )
 
 
+class ClearUserSyncsCommand(Command):
+    """Sent by the client to inform the server that it should drop all
+    information about syncing users sent by the client.
+
+    Mainly used when client is about to shut down.
+
+    Format::
+
+        CLEAR_USER_SYNC <instance_id>
+    """
+
+    NAME = "CLEAR_USER_SYNC"
+
+    def __init__(self, instance_id):
+        self.instance_id = instance_id
+
+    @classmethod
+    def from_line(cls, line):
+        return cls(line)
+
+    def to_line(self):
+        return self.instance_id
+
+
 class FederationAckCommand(Command):
     """Sent by the client when it has processed up to a given point in the
     federation stream. This allows the master to drop in-memory caches of the
@@ -398,6 +424,7 @@ _COMMANDS = (
     InvalidateCacheCommand,
     UserIpCommand,
     RemoteServerUpCommand,
+    ClearUserSyncsCommand,
 )  # type: Tuple[Type[Command], ...]
 
 # Map of command name to command type.
@@ -420,6 +447,7 @@ VALID_CLIENT_COMMANDS = (
     ReplicateCommand.NAME,
     PingCommand.NAME,
     UserSyncCommand.NAME,
+    ClearUserSyncsCommand.NAME,
     FederationAckCommand.NAME,
     RemovePusherCommand.NAME,
     InvalidateCacheCommand.NAME,
diff --git a/synapse/replication/tcp/protocol.py b/synapse/replication/tcp/protocol.py
index f81d2e2442..dae246825f 100644
--- a/synapse/replication/tcp/protocol.py
+++ b/synapse/replication/tcp/protocol.py
@@ -423,9 +423,12 @@ class ServerReplicationStreamProtocol(BaseReplicationStreamProtocol):
 
     async def on_USER_SYNC(self, cmd):
         await self.streamer.on_user_sync(
-            self.conn_id, cmd.user_id, cmd.is_syncing, cmd.last_sync_ms
+            cmd.instance_id, cmd.user_id, cmd.is_syncing, cmd.last_sync_ms
         )
 
+    async def on_CLEAR_USER_SYNC(self, cmd):
+        await self.streamer.on_clear_user_syncs(cmd.instance_id)
+
     async def on_REPLICATE(self, cmd):
         # Subscribe to all streams we're publishing to.
         for stream_name in self.streamer.streams_by_name:
@@ -551,6 +554,8 @@ class ClientReplicationStreamProtocol(BaseReplicationStreamProtocol):
     ):
         BaseReplicationStreamProtocol.__init__(self, clock)
 
+        self.instance_id = hs.get_instance_id()
+
         self.client_name = client_name
         self.server_name = server_name
         self.handler = handler
@@ -580,7 +585,7 @@ class ClientReplicationStreamProtocol(BaseReplicationStreamProtocol):
         currently_syncing = self.handler.get_currently_syncing_users()
         now = self.clock.time_msec()
         for user_id in currently_syncing:
-            self.send_command(UserSyncCommand(user_id, True, now))
+            self.send_command(UserSyncCommand(self.instance_id, user_id, True, now))
 
         # We've now finished connecting to so inform the client handler
         self.handler.update_connection(self)
diff --git a/synapse/replication/tcp/resource.py b/synapse/replication/tcp/resource.py
index 4374e99e32..8b6067e20d 100644
--- a/synapse/replication/tcp/resource.py
+++ b/synapse/replication/tcp/resource.py
@@ -251,14 +251,19 @@ class ReplicationStreamer(object):
             self.federation_sender.federation_ack(token)
 
     @measure_func("repl.on_user_sync")
-    async def on_user_sync(self, conn_id, user_id, is_syncing, last_sync_ms):
+    async def on_user_sync(self, instance_id, user_id, is_syncing, last_sync_ms):
         """A client has started/stopped syncing on a worker.
         """
         user_sync_counter.inc()
         await self.presence_handler.update_external_syncs_row(
-            conn_id, user_id, is_syncing, last_sync_ms
+            instance_id, user_id, is_syncing, last_sync_ms
         )
 
+    async def on_clear_user_syncs(self, instance_id):
+        """A replication client wants us to drop all their UserSync data.
+        """
+        await self.presence_handler.update_external_syncs_clear(instance_id)
+
     @measure_func("repl.on_remove_pusher")
     async def on_remove_pusher(self, app_id, push_key, user_id):
         """A client has asked us to remove a pusher
@@ -321,14 +326,6 @@ class ReplicationStreamer(object):
         except ValueError:
             pass
 
-        # We need to tell the presence handler that the connection has been
-        # lost so that it can handle any ongoing syncs on that connection.
-        run_as_background_process(
-            "update_external_syncs_clear",
-            self.presence_handler.update_external_syncs_clear,
-            connection.conn_id,
-        )
-
 
 def _batch_updates(updates):
     """Takes a list of updates of form [(token, row)] and sets the token to