Move catchup of replication streams to worker. (matrix-org#7024)

This changes the replication protocol so that the server does not send down `RDATA` for rows that happened before the client connected. Instead, the server will send a `POSITION` and clients then query the database (or master out of band) to get up to date.

changelog.d/7024.misc

@@ -0,0 +1 @@
+Move catchup of replication streams logic to worker.

docs/tcp_replication.md

@@ -14,16 +14,16 @@ example flow would be (where '>' indicates master to worker and
 '<' worker to master flows):
 
     > SERVER example.com
-    < REPLICATE events 53
+    < REPLICATE
+    > POSITION events 53
     > RDATA events 54 ["$foo1:bar.com", ...]
     > RDATA events 55 ["$foo4:bar.com", ...]
 
-The example shows the server accepting a new connection and sending its
-identity with the `SERVER` command, followed by the client asking to
-subscribe to the `events` stream from the token `53`. 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.
+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.
 
 Error reporting happens by either the client or server sending an ERROR
 command, and usually the connection will be closed.
@@ -32,9 +32,6 @@ Since the protocol is a simple line based, its possible to manually
 connect to the server using a tool like netcat. A few things should be
 noted when manually using the protocol:
 
--   When subscribing to a stream using `REPLICATE`, the special token
-    `NOW` can be used to get all future updates. The special stream name
-    `ALL` can be used with `NOW` to subscribe to all available streams.
 -   The federation stream is only available if federation sending has
     been disabled on the main process.
 -   The server will only time connections out that have sent a `PING`
@@ -91,9 +88,7 @@ The client:
 -   Sends a `NAME` command, allowing the server to associate a human
     friendly name with the connection. This is optional.
 -   Sends a `PING` as above
--   For each stream the client wishes to subscribe to it sends a
-    `REPLICATE` with the `stream_name` and token it wants to subscribe
-    from.
+-   Sends a `REPLICATE` to get the current position of all streams.
 -   On receipt of a `SERVER` command, checks that the server name
     matches the expected server name.
 
@@ -140,9 +135,7 @@ the wire:
     > PING 1490197665618
     < NAME synapse.app.appservice
     < PING 1490197665618
-    < REPLICATE events 1
-    < REPLICATE backfill 1
-    < REPLICATE caches 1
+    < REPLICATE
     > POSITION events 1
     > POSITION backfill 1
     > POSITION caches 1
@@ -181,9 +174,9 @@ client (C):
 
 #### POSITION (S)
 
-   The position of the stream has been updated. Sent to the client
-    after all missing updates for a stream have been sent to the client
-    and they're now up to date.
+   On receipt of a POSITION command clients should check if they have missed any
+   updates, and if so then fetch them out of band. Sent in response to a
+   REPLICATE command (but can happen at any time).
 
 #### ERROR (S, C)
 
@@ -199,20 +192,7 @@ client (C):
 
 #### REPLICATE (C)
 
-Asks the server to replicate a given stream. The syntax is:
-
-```
-    REPLICATE <stream_name> <token>
-```
-
-Where `<token>` may be either:
- * a numeric stream_id to stream updates since (exclusive)
- * `NOW` to stream all subsequent updates.
-
-The `<stream_name>` is the name of a replication stream to subscribe
-to (see [here](../synapse/replication/tcp/streams/_base.py) for a list
-of streams). It can also be `ALL` to subscribe to all known streams,
-in which case the `<token>` must be set to `NOW`.
+Asks the server for the current position of all streams.
 
 #### USER_SYNC (C)
 

synapse/app/generic_worker.py

@@ -405,6 +405,9 @@ def process_replication_rows(self, token, rows):
             self._room_serials[row.room_id] = token
             self._room_typing[row.room_id] = row.user_ids
 
+    def get_current_token(self) -> int:
+        return self._latest_room_serial
+
 
 class GenericWorkerSlavedStore(
     # FIXME(#3714): We need to add UserDirectoryStore as we write directly

synapse/federation/sender/__init__.py

@@ -499,4 +499,13 @@ def wake_destination(self, destination: str):
         self._get_per_destination_queue(destination).attempt_new_transaction()
 
     def get_current_token(self) -> int:
+        # Dummy implementation for case where federation sender isn't offloaded
+        # to a worker.
         return 0
+
+    async def get_replication_rows(
+        self, from_token, to_token, limit, federation_ack=None
+    ):
+        # Dummy implementation for case where federation sender isn't offloaded
+        # to a worker.
+        return []

synapse/replication/http/__init__.py

@@ -21,6 +21,7 @@
     membership,
     register,
     send_event,
+    streams,
 )
 
 REPLICATION_PREFIX = "/_synapse/replication"
@@ -38,3 +39,4 @@ def register_servlets(self, hs):
         login.register_servlets(hs, self)
         register.register_servlets(hs, self)
         devices.register_servlets(hs, self)
+        streams.register_servlets(hs, self)

synapse/replication/http/streams.py

@@ -0,0 +1,78 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+# 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.
+
+import logging
+
+from synapse.api.errors import SynapseError
+from synapse.http.servlet import parse_integer
+from synapse.replication.http._base import ReplicationEndpoint
+
+logger = logging.getLogger(__name__)
+
+
+class ReplicationGetStreamUpdates(ReplicationEndpoint):
+    """Fetches stream updates from a server. Used for streams not persisted to
+    the database, e.g. typing notifications.
+
+    The API looks like:
+
+        GET /_synapse/replication/get_repl_stream_updates/events?from_token=0&to_token=10&limit=100
+
+        200 OK
+
+        {
+            updates: [ ... ],
+            upto_token: 10,
+            limited: False,
+        }
+
+    """
+
+    NAME = "get_repl_stream_updates"
+    PATH_ARGS = ("stream_name",)
+    METHOD = "GET"
+
+    def __init__(self, hs):
+        super().__init__(hs)
+
+        # We pull the streams from the replication steamer (if we try and make
+        # them ourselves we end up in an import loop).
+        self.streams = hs.get_replication_streamer().get_streams()
+
+    @staticmethod
+    def _serialize_payload(stream_name, from_token, upto_token, limit):
+        return {"from_token": from_token, "upto_token": upto_token, "limit": limit}
+
+    async def _handle_request(self, request, stream_name):
+        stream = self.streams.get(stream_name)
+        if stream is None:
+            raise SynapseError(400, "Unknown stream")
+
+        from_token = parse_integer(request, "from_token", required=True)
+        upto_token = parse_integer(request, "upto_token", required=True)
+        limit = parse_integer(request, "limit", required=True)
+
+        updates, upto_token, limited = await stream.get_updates_since(
+            from_token, upto_token, limit
+        )
+
+        return (
+            200,
+            {"updates": updates, "upto_token": upto_token, "limited": limited},
+        )
+
+
+def register_servlets(hs, http_server):
+    ReplicationGetStreamUpdates(hs).register(http_server)

synapse/replication/slave/storage/_base.py

@@ -18,8 +18,10 @@
 
 import six
 
-from synapse.storage._base import SQLBaseStore
-from synapse.storage.data_stores.main.cache import CURRENT_STATE_CACHE_NAME
+from synapse.storage.data_stores.main.cache import (
+    CURRENT_STATE_CACHE_NAME,
+    CacheInvalidationWorkerStore,
+)
 from synapse.storage.database import Database
 from synapse.storage.engines import PostgresEngine
 
@@ -35,7 +37,7 @@ def __func__(inp):
         return inp.__func__
 
 
-class BaseSlavedStore(SQLBaseStore):
+class BaseSlavedStore(CacheInvalidationWorkerStore):
     def __init__(self, database: Database, db_conn, hs):
         super(BaseSlavedStore, self).__init__(database, db_conn, hs)
         if isinstance(self.database_engine, PostgresEngine):
@@ -60,6 +62,12 @@ def stream_positions(self) -> Dict[str, int]:
             pos["caches"] = self._cache_id_gen.get_current_token()
         return pos
 
+    def get_cache_stream_token(self):
+        if self._cache_id_gen:
+            return self._cache_id_gen.get_current_token()
+        else:
+            return 0
+
     def process_replication_rows(self, stream_name, token, rows):
         if stream_name == "caches":
             if self._cache_id_gen:

synapse/replication/slave/storage/pushers.py

@@ -33,6 +33,9 @@ def stream_positions(self):
         result["pushers"] = self._pushers_id_gen.get_current_token()
         return result
 
+    def get_pushers_stream_token(self):
+        return self._pushers_id_gen.get_current_token()
+
     def process_replication_rows(self, stream_name, token, rows):
         if stream_name == "pushers":
             self._pushers_id_gen.advance(token)

synapse/replication/tcp/client.py

@@ -55,6 +55,7 @@ def __init__(self, hs, client_name, handler: AbstractReplicationClientHandler):
         self.client_name = client_name
         self.handler = handler
         self.server_name = hs.config.server_name
+        self.hs = hs
         self._clock = hs.get_clock()  # As self.clock is defined in super class
 
         hs.get_reactor().addSystemEventTrigger("before", "shutdown", self.stopTrying)
@@ -65,7 +66,7 @@ def startedConnecting(self, connector):
     def buildProtocol(self, addr):
         logger.info("Connected to replication: %r", addr)
         return ClientReplicationStreamProtocol(
-            self.client_name, self.server_name, self._clock, self.handler
+            self.hs, self.client_name, self.server_name, self._clock, self.handler,
         )
 
     def clientConnectionLost(self, connector, reason):

synapse/replication/tcp/commands.py

@@ -136,8 +136,8 @@ class PositionCommand(Command):
     """Sent by the server to tell the client the stream postition without
     needing to send an RDATA.
 
-    Sent to the client after all missing updates for a stream have been sent
-    to the client and they're now up to date.
+    On receipt of a POSITION command clients should check if they have missed
+    any updates, and if so then fetch them out of band.
     """
 
     NAME = "POSITION"
@@ -179,42 +179,24 @@ class NameCommand(Command):
 
 
 class ReplicateCommand(Command):
-    """Sent by the client to subscribe to the stream.
+    """Sent by the client to subscribe to streams.
 
     Format::
 
-        REPLICATE <stream_name> <token>
-
-    Where <token> may be either:
-        * a numeric stream_id to stream updates from
-        * "NOW" to stream all subsequent updates.
-
-    The <stream_name> can be "ALL" to subscribe to all known streams, in which
-    case the <token> must be set to "NOW", i.e.::
-
-        REPLICATE ALL NOW
+        REPLICATE
     """
 
     NAME = "REPLICATE"
 
-    def __init__(self, stream_name, token):
-        self.stream_name = stream_name
-        self.token = token
+    def __init__(self):
+        pass
 
     @classmethod
     def from_line(cls, line):
-        stream_name, token = line.split(" ", 1)
-        if token in ("NOW", "now"):
-            token = "NOW"
-        else:
-            token = int(token)
-        return cls(stream_name, token)
+        return cls()
 
     def to_line(self):
-        return " ".join((self.stream_name, str(self.token)))
-
-    def get_logcontext_id(self):
-        return "REPLICATE-" + self.stream_name
+        return ""
 
 
 class UserSyncCommand(Command):