Move catchup of replication streams to worker. (#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.

1 files changed, 8 insertions, 26 deletions

diff --git a/synapse/replication/tcp/commands.py b/synapse/replication/tcp/commands.py
index 451671412d..5a6b734094 100644
--- a/synapse/replication/tcp/commands.py
+++ b/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):