Add instance name to RDATA/POSITION commands

changelog.d/7364.misc

@@ -0,0 +1 @@
+Add an `instance_name` to `RDATA` and `POSITION` replication commands.

docs/tcp_replication.md

@@ -15,15 +15,17 @@ example flow would be (where '>' indicates master to worker and
 
     > SERVER example.com
     < REPLICATE
-    > POSITION events 53
-    > RDATA events 54 ["$foo1:bar.com", ...]
-    > RDATA events 55 ["$foo4:bar.com", ...]
+    > POSITION events master 53
+    > RDATA events master 54 ["$foo1:bar.com", ...]
+    > RDATA events master 55 ["$foo4:bar.com", ...]
 
 The example shows the server accepting a new connection and sending its identity
 with the `SERVER` command, followed by the client server to respond with the
 position of all streams. The server then periodically sends `RDATA` commands
-which have the format `RDATA <stream_name> <token> <row>`, where the format of
-`<row>` is defined by the individual streams.
+which have the format `RDATA <stream_name> <instance_name> <token> <row>`, where
+the format of `<row>` is defined by the individual streams. The
+`<instance_name>` is the name of the Synapse process that generated the data
+(e.g. usually "master").
 
 Error reporting happens by either the client or server sending an ERROR
 command, and usually the connection will be closed.
@@ -52,7 +54,7 @@ The basic structure of the protocol is line based, where the initial
 word of each line specifies the command. The rest of the line is parsed
 based on the command. For example, the RDATA command is defined as:
 
-    RDATA <stream_name> <token> <row_json>
+    RDATA <stream_name> <instance_name> <token> <row_json>
 
 (Note that <row_json> may contains spaces, but cannot contain
 newlines.)
@@ -136,11 +138,11 @@ the wire:
     < NAME synapse.app.appservice
     < PING 1490197665618
     < REPLICATE
-    > POSITION events 1
-    > POSITION backfill 1
-    > POSITION caches 1
-    > RDATA caches 2 ["get_user_by_id",["@01register-user:localhost:8823"],1490197670513]
-    > RDATA events 14 ["$149019767112vOHxz:localhost:8823",
+    > POSITION events master 1
+    > POSITION backfill master 1
+    > POSITION caches master 1
+    > RDATA caches master 2 ["get_user_by_id",["@01register-user:localhost:8823"],1490197670513]
+    > RDATA events master 14 ["$149019767112vOHxz:localhost:8823",
         "!AFDCvgApUmpdfVjIXm:localhost:8823","m.room.guest_access","",null]
     < PING 1490197675618
     > ERROR server stopping
@@ -151,10 +153,10 @@ position without needing to send data with the `RDATA` command.
 
 An example of a batched set of `RDATA` is:
 
-    > RDATA caches batch ["get_user_by_id",["@test:localhost:8823"],1490197670513]
-    > RDATA caches batch ["get_user_by_id",["@test2:localhost:8823"],1490197670513]
-    > RDATA caches batch ["get_user_by_id",["@test3:localhost:8823"],1490197670513]
-    > RDATA caches 54 ["get_user_by_id",["@test4:localhost:8823"],1490197670513]
+    > RDATA caches master batch ["get_user_by_id",["@test:localhost:8823"],1490197670513]
+    > RDATA caches master batch ["get_user_by_id",["@test2:localhost:8823"],1490197670513]
+    > RDATA caches master batch ["get_user_by_id",["@test3:localhost:8823"],1490197670513]
+    > RDATA caches master 54 ["get_user_by_id",["@test4:localhost:8823"],1490197670513]
 
 In this case the client shouldn't advance their caches token until it
 sees the the last `RDATA`.
@@ -178,6 +180,11 @@ client (C):
    updates, and if so then fetch them out of band. Sent in response to a
    REPLICATE command (but can happen at any time).
 
+   The POSITION command includes the source of the stream. Currently all streams
+   are written by a single process (usually "master"). If fetching missing
+   updates via HTTP API, rather than via the DB, then processes should make the
+   request to the appropriate process.
+
 #### ERROR (S, C)
 
    There was an error
@@ -234,12 +241,12 @@ Each individual cache invalidation results in a row being sent down
 replication, which includes the cache name (the name of the function)
 and they key to invalidate. For example:
 
-    > RDATA caches 550953771 ["get_user_by_id", ["@bob:example.com"], 1550574873251]
+    > RDATA caches master 550953771 ["get_user_by_id", ["@bob:example.com"], 1550574873251]
 
 Alternatively, an entire cache can be invalidated by sending down a `null`
 instead of the key. For example:
 
-    > RDATA caches 550953772 ["get_user_by_id", null, 1550574873252]
+    > RDATA caches master 550953772 ["get_user_by_id", null, 1550574873252]
 
 However, there are times when a number of caches need to be invalidated
 at the same time with the same key. To reduce traffic we batch those

synapse/replication/tcp/commands.py

@@ -95,7 +95,7 @@ class RdataCommand(Command):
 
     Format::
 
-        RDATA <stream_name> <token> <row_json>
+        RDATA <stream_name> <instance_name> <token> <row_json>
 
     The `<token>` may either be a numeric stream id OR "batch". The latter case
     is used to support sending multiple updates with the same stream ID. This
@@ -105,33 +105,40 @@ class RdataCommand(Command):
     The client should batch all incoming RDATA with a token of "batch" (per
     stream_name) until it sees an RDATA with a numeric stream ID.
 
+    The `<instance_name>` is the source of the new data (usually "master").
+
     `<token>` of "batch" maps to the instance variable `token` being None.
 
     An example of a batched series of RDATA::
 
-        RDATA presence batch ["@foo:example.com", "online", ...]
-        RDATA presence batch ["@bar:example.com", "online", ...]
-        RDATA presence 59 ["@baz:example.com", "online", ...]
+        RDATA presence master batch ["@foo:example.com", "online", ...]
+        RDATA presence master batch ["@bar:example.com", "online", ...]
+        RDATA presence master 59 ["@baz:example.com", "online", ...]
     """
 
     NAME = "RDATA"
 
-    def __init__(self, stream_name, token, row):
+    def __init__(self, stream_name, instance_name, token, row):
         self.stream_name = stream_name
+        self.instance_name = instance_name
         self.token = token
         self.row = row
 
     @classmethod
     def from_line(cls, line):
-        stream_name, token, row_json = line.split(" ", 2)
+        stream_name, instance_name, token, row_json = line.split(" ", 3)
         return cls(
-            stream_name, None if token == "batch" else int(token), json.loads(row_json)
+            stream_name,
+            instance_name,
+            None if token == "batch" else int(token),
+            json.loads(row_json),
         )
 
     def to_line(self):
         return " ".join(
             (
                 self.stream_name,
+                self.instance_name,
                 str(self.token) if self.token is not None else "batch",
                 _json_encoder.encode(self.row),
             )
@@ -145,23 +152,31 @@ class PositionCommand(Command):
     """Sent by the server to tell the client the stream postition without
     needing to send an RDATA.
 
+    Format::
+
+        POSITION <stream_name> <instance_name> <token>
+
     On receipt of a POSITION command clients should check if they have missed
     any updates, and if so then fetch them out of band.
+
+    The `<instance_name>` is the process that sent the command and is the source
+    of the stream.
     """
 
     NAME = "POSITION"
 
-    def __init__(self, stream_name, token):
+    def __init__(self, stream_name, instance_name, token):
         self.stream_name = stream_name
+        self.instance_name = instance_name
         self.token = token
 
     @classmethod
     def from_line(cls, line):
-        stream_name, token = line.split(" ", 1)
-        return cls(stream_name, int(token))
+        stream_name, instance_name, token = line.split(" ", 2)
+        return cls(stream_name, instance_name, int(token))
 
     def to_line(self):
-        return " ".join((self.stream_name, str(self.token)))
+        return " ".join((self.stream_name, self.instance_name, str(self.token)))
 
 
 class ErrorCommand(_SimpleCommand):

synapse/replication/tcp/handler.py

@@ -79,6 +79,7 @@ def __init__(self, hs):
         self._notifier = hs.get_notifier()
         self._clock = hs.get_clock()
         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]
@@ -169,7 +170,9 @@ async def on_REPLICATE(self, cmd: ReplicateCommand):
 
         for stream_name, stream in self._streams.items():
             current_token = stream.current_token()
-            self.send_command(PositionCommand(stream_name, current_token))
+            self.send_command(
+                PositionCommand(stream_name, self._instance_name, current_token)
+            )
 
     async def on_USER_SYNC(self, cmd: UserSyncCommand):
         user_sync_counter.inc()
@@ -226,6 +229,10 @@ async def on_USER_IP(self, cmd: UserIpCommand):
             await self._server_notices_sender.on_user_ip(cmd.user_id)
 
     async def on_RDATA(self, cmd: RdataCommand):
+        if cmd.instance_name == self._instance_name:
+            # Ignore RDATA that are just our own echoes
+            return
+
         stream_name = cmd.stream_name
         inbound_rdata_count.labels(stream_name).inc()
 
@@ -277,6 +284,10 @@ async def on_rdata(self, stream_name: str, token: int, rows: list):
         await self._replication_data_handler.on_rdata(stream_name, token, rows)
 
     async def on_POSITION(self, cmd: PositionCommand):
+        if cmd.instance_name == self._instance_name:
+            # Ignore RDATA that are just our own echoes
+            return
+
         stream = self._streams.get(cmd.stream_name)
         if not stream:
             logger.error("Got POSITION for unknown stream: %s", cmd.stream_name)
@@ -448,7 +459,7 @@ def stream_update(self, stream_name: str, token: str, data: Any):
 
         We need to check if the client is interested in the stream or not
         """
-        self.send_command(RdataCommand(stream_name, token, data))
+        self.send_command(RdataCommand(stream_name, self._instance_name, token, data))
 
 
 UpdateToken = TypeVar("UpdateToken")

synapse/server.py

@@ -235,6 +235,7 @@ def __init__(self, hostname: str, config: HomeServerConfig, reactor=None, **kwar
         self.start_time = None
 
         self.instance_id = random_string(5)
+        self.instance_name = config.worker_name or "master"
 
         self.clock = Clock(reactor)
         self.distributor = Distributor()
@@ -256,6 +257,14 @@ def get_instance_id(self):
         """
         return self.instance_id
 
+    def get_instance_name(self) -> str:
+        """A unique name for this synapse process.
+
+        Used to identify the process over replication and in config. Does not
+        change over restarts.
+        """
+        return self.instance_name
+
     def setup(self):
         logger.info("Setting up.")
         self.start_time = int(self.get_clock().time())

synapse/server.pyi

@@ -121,3 +121,5 @@ class HomeServer(object):
         pass
     def get_instance_id(self) -> str:
         pass
+    def get_instance_name(self) -> str:
+        pass

tests/replication/slave/storage/_base.py

@@ -57,6 +57,7 @@ def prepare(self, reactor, clock, hs):
         # We now do some gut wrenching so that we have a client that is based
         # off of the slave store rather than the main store.
         self.replication_handler = ReplicationCommandHandler(self.hs)
+        self.replication_handler._instance_name = "worker"
         self.replication_handler._replication_data_handler = ReplicationDataHandler(
             self.slaved_store
         )

tests/replication/tcp/test_commands.py

@@ -28,15 +28,17 @@ def test_parse_one_word_command(self):
         self.assertIsInstance(cmd, ReplicateCommand)
 
     def test_parse_rdata(self):
-        line = 'RDATA events 6287863 ["ev", ["$eventid", "!roomid", "type", null, null, null]]'
+        line = 'RDATA events master 6287863 ["ev", ["$eventid", "!roomid", "type", null, null, null]]'
         cmd = parse_command_from_line(line)
         self.assertIsInstance(cmd, RdataCommand)
         self.assertEqual(cmd.stream_name, "events")
+        self.assertEqual(cmd.instance_name, "master")
         self.assertEqual(cmd.token, 6287863)
 
     def test_parse_rdata_batch(self):
-        line = 'RDATA presence batch ["@foo:example.com", "online"]'
+        line = 'RDATA presence master batch ["@foo:example.com", "online"]'
         cmd = parse_command_from_line(line)
         self.assertIsInstance(cmd, RdataCommand)
         self.assertEqual(cmd.stream_name, "presence")
+        self.assertEqual(cmd.instance_name, "master")
         self.assertIsNone(cmd.token)