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document the REPLICATE command a bit better (#6305)
since I found myself wonder how it works
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5 changed files with 110 additions and 10 deletions
1
changelog.d/6305.misc
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1
changelog.d/6305.misc
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@ -0,0 +1 @@
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Add some documentation about worker replication.
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@ -199,7 +199,20 @@ client (C):
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#### REPLICATE (C)
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Asks the server to replicate a given stream
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Asks the server to replicate a given stream. The syntax is:
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```
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REPLICATE <stream_name> <token>
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```
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Where `<token>` may be either:
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* a numeric stream_id to stream updates since (exclusive)
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* `NOW` to stream all subsequent updates.
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The `<stream_name>` is the name of a replication stream to subscribe
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to (see [here](../synapse/replication/tcp/streams/_base.py) for a list
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of streams). It can also be `ALL` to subscribe to all known streams,
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in which case the `<token>` must be set to `NOW`.
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#### USER_SYNC (C)
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@ -14,6 +14,7 @@
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# limitations under the License.
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import logging
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from typing import Dict
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import six
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@ -44,7 +45,14 @@ class BaseSlavedStore(SQLBaseStore):
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self.hs = hs
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def stream_positions(self):
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def stream_positions(self) -> Dict[str, int]:
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"""
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Get the current positions of all the streams this store wants to subscribe to
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Returns:
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map from stream name to the most recent update we have for
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that stream (ie, the point we want to start replicating from)
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"""
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pos = {}
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if self._cache_id_gen:
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pos["caches"] = self._cache_id_gen.get_current_token()
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@ -16,10 +16,17 @@
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"""
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import logging
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from typing import Dict
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from twisted.internet import defer
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from twisted.internet.protocol import ReconnectingClientFactory
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from synapse.replication.slave.storage._base import BaseSlavedStore
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from synapse.replication.tcp.protocol import (
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AbstractReplicationClientHandler,
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ClientReplicationStreamProtocol,
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)
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from .commands import (
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FederationAckCommand,
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InvalidateCacheCommand,
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@ -27,7 +34,6 @@ from .commands import (
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UserIpCommand,
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UserSyncCommand,
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)
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from .protocol import ClientReplicationStreamProtocol
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logger = logging.getLogger(__name__)
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@ -42,7 +48,7 @@ class ReplicationClientFactory(ReconnectingClientFactory):
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maxDelay = 30 # Try at least once every N seconds
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def __init__(self, hs, client_name, handler):
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def __init__(self, hs, client_name, handler: AbstractReplicationClientHandler):
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self.client_name = client_name
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self.handler = handler
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self.server_name = hs.config.server_name
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@ -68,13 +74,13 @@ class ReplicationClientFactory(ReconnectingClientFactory):
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ReconnectingClientFactory.clientConnectionFailed(self, connector, reason)
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class ReplicationClientHandler(object):
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class ReplicationClientHandler(AbstractReplicationClientHandler):
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"""A base handler that can be passed to the ReplicationClientFactory.
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By default proxies incoming replication data to the SlaveStore.
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"""
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def __init__(self, store):
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def __init__(self, store: BaseSlavedStore):
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self.store = store
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# The current connection. None if we are currently (re)connecting
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@ -138,11 +144,13 @@ class ReplicationClientHandler(object):
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if d:
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d.callback(data)
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def get_streams_to_replicate(self):
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def get_streams_to_replicate(self) -> Dict[str, int]:
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"""Called when a new connection has been established and we need to
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subscribe to streams.
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Returns a dictionary of stream name to token.
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Returns:
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map from stream name to the most recent update we have for
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that stream (ie, the point we want to start replicating from)
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"""
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args = self.store.stream_positions()
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user_account_data = args.pop("user_account_data", None)
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@ -48,7 +48,7 @@ indicate which side is sending, these are *not* included on the wire::
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> ERROR server stopping
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* connection closed by server *
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"""
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import abc
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import fcntl
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import logging
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import struct
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@ -65,6 +65,7 @@ from twisted.python.failure import Failure
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from synapse.logging.context import make_deferred_yieldable, run_in_background
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from synapse.metrics import LaterGauge
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from synapse.metrics.background_process_metrics import run_as_background_process
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from synapse.util import Clock
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from synapse.util.stringutils import random_string
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from .commands import (
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@ -558,11 +559,80 @@ class ServerReplicationStreamProtocol(BaseReplicationStreamProtocol):
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self.streamer.lost_connection(self)
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class AbstractReplicationClientHandler(metaclass=abc.ABCMeta):
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"""
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The interface for the handler that should be passed to
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ClientReplicationStreamProtocol
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"""
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@abc.abstractmethod
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def on_rdata(self, stream_name, token, rows):
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"""Called to handle a batch of replication data with a given stream token.
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Args:
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stream_name (str): name of the replication stream for this batch of rows
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token (int): stream token for this batch of rows
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rows (list): a list of Stream.ROW_TYPE objects as returned by
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Stream.parse_row.
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Returns:
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Deferred|None
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"""
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raise NotImplementedError()
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@abc.abstractmethod
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def on_position(self, stream_name, token):
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"""Called when we get new position data."""
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raise NotImplementedError()
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@abc.abstractmethod
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def on_sync(self, data):
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"""Called when get a new SYNC command."""
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raise NotImplementedError()
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@abc.abstractmethod
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def get_streams_to_replicate(self):
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"""Called when a new connection has been established and we need to
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subscribe to streams.
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Returns:
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map from stream name to the most recent update we have for
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that stream (ie, the point we want to start replicating from)
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"""
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raise NotImplementedError()
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@abc.abstractmethod
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def get_currently_syncing_users(self):
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"""Get the list of currently syncing users (if any). This is called
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when a connection has been established and we need to send the
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currently syncing users."""
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raise NotImplementedError()
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@abc.abstractmethod
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def update_connection(self, connection):
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"""Called when a connection has been established (or lost with None).
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"""
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raise NotImplementedError()
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@abc.abstractmethod
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def finished_connecting(self):
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"""Called when we have successfully subscribed and caught up to all
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streams we're interested in.
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"""
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raise NotImplementedError()
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class ClientReplicationStreamProtocol(BaseReplicationStreamProtocol):
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VALID_INBOUND_COMMANDS = VALID_SERVER_COMMANDS
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VALID_OUTBOUND_COMMANDS = VALID_CLIENT_COMMANDS
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def __init__(self, client_name, server_name, clock, handler):
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def __init__(
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self,
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client_name: str,
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server_name: str,
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clock: Clock,
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handler: AbstractReplicationClientHandler,
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):
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BaseReplicationStreamProtocol.__init__(self, clock)
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self.client_name = client_name
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