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https://mau.dev/maunium/synapse.git
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1531b214fc
The idea here is that if an instance persists an event via the replication HTTP API it can return before we receive that event over replication, which can lead to races where code assumes that persisting an event immediately updates various caches (e.g. current state of the room). Most of Synapse doesn't hit such races, so we don't do the waiting automagically, instead we do so where necessary to avoid unnecessary delays. We may decide to change our minds here if it turns out there are a lot of subtle races going on. People probably want to look at this commit by commit.
225 lines
8.8 KiB
Python
225 lines
8.8 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2017 Vector Creations Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""A replication client for use by synapse workers.
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"""
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import heapq
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import logging
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from typing import TYPE_CHECKING, Dict, List, Tuple
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from twisted.internet.defer import Deferred
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from twisted.internet.protocol import ReconnectingClientFactory
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from synapse.api.constants import EventTypes
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from synapse.logging.context import PreserveLoggingContext, make_deferred_yieldable
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from synapse.replication.tcp.protocol import ClientReplicationStreamProtocol
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from synapse.replication.tcp.streams.events import (
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EventsStream,
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EventsStreamEventRow,
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EventsStreamRow,
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)
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from synapse.util.async_helpers import timeout_deferred
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from synapse.util.metrics import Measure
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if TYPE_CHECKING:
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from synapse.server import HomeServer
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from synapse.replication.tcp.handler import ReplicationCommandHandler
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logger = logging.getLogger(__name__)
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# How long we allow callers to wait for replication updates before timing out.
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_WAIT_FOR_REPLICATION_TIMEOUT_SECONDS = 30
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class DirectTcpReplicationClientFactory(ReconnectingClientFactory):
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"""Factory for building connections to the master. Will reconnect if the
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connection is lost.
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Accepts a handler that is passed to `ClientReplicationStreamProtocol`.
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"""
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initialDelay = 0.1
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maxDelay = 1 # Try at least once every N seconds
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def __init__(
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self,
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hs: "HomeServer",
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client_name: str,
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command_handler: "ReplicationCommandHandler",
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):
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self.client_name = client_name
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self.command_handler = command_handler
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self.server_name = hs.config.server_name
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self.hs = hs
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self._clock = hs.get_clock() # As self.clock is defined in super class
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hs.get_reactor().addSystemEventTrigger("before", "shutdown", self.stopTrying)
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def startedConnecting(self, connector):
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logger.info("Connecting to replication: %r", connector.getDestination())
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def buildProtocol(self, addr):
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logger.info("Connected to replication: %r", addr)
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return ClientReplicationStreamProtocol(
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self.hs,
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self.client_name,
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self.server_name,
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self._clock,
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self.command_handler,
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)
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def clientConnectionLost(self, connector, reason):
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logger.error("Lost replication conn: %r", reason)
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ReconnectingClientFactory.clientConnectionLost(self, connector, reason)
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def clientConnectionFailed(self, connector, reason):
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logger.error("Failed to connect to replication: %r", reason)
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ReconnectingClientFactory.clientConnectionFailed(self, connector, reason)
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class ReplicationDataHandler:
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"""Handles incoming stream updates from replication.
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This instance notifies the slave data store about updates. Can be subclassed
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to handle updates in additional ways.
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"""
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def __init__(self, hs: "HomeServer"):
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self.store = hs.get_datastore()
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self.pusher_pool = hs.get_pusherpool()
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self.notifier = hs.get_notifier()
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self._reactor = hs.get_reactor()
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self._clock = hs.get_clock()
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self._streams = hs.get_replication_streams()
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self._instance_name = hs.get_instance_name()
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# Map from stream to list of deferreds waiting for the stream to
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# arrive at a particular position. The lists are sorted by stream position.
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self._streams_to_waiters = (
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{}
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) # type: Dict[str, List[Tuple[int, Deferred[None]]]]
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async def on_rdata(
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self, stream_name: str, instance_name: str, token: int, rows: list
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):
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"""Called to handle a batch of replication data with a given stream token.
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By default this just pokes the slave store. Can be overridden in subclasses to
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handle more.
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Args:
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stream_name: name of the replication stream for this batch of rows
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instance_name: the instance that wrote the rows.
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token: stream token for this batch of rows
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rows: a list of Stream.ROW_TYPE objects as returned by Stream.parse_row.
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"""
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self.store.process_replication_rows(stream_name, instance_name, token, rows)
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if stream_name == EventsStream.NAME:
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# We shouldn't get multiple rows per token for events stream, so
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# we don't need to optimise this for multiple rows.
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for row in rows:
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if row.type != EventsStreamEventRow.TypeId:
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continue
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assert isinstance(row, EventsStreamRow)
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event = await self.store.get_event(
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row.data.event_id, allow_rejected=True
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)
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if event.rejected_reason:
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continue
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extra_users = () # type: Tuple[str, ...]
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if event.type == EventTypes.Member:
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extra_users = (event.state_key,)
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max_token = self.store.get_room_max_stream_ordering()
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self.notifier.on_new_room_event(event, token, max_token, extra_users)
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await self.pusher_pool.on_new_notifications(token, token)
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# Notify any waiting deferreds. The list is ordered by position so we
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# just iterate through the list until we reach a position that is
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# greater than the received row position.
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waiting_list = self._streams_to_waiters.get(stream_name, [])
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# Index of first item with a position after the current token, i.e we
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# have called all deferreds before this index. If not overwritten by
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# loop below means either a) no items in list so no-op or b) all items
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# in list were called and so the list should be cleared. Setting it to
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# `len(list)` works for both cases.
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index_of_first_deferred_not_called = len(waiting_list)
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for idx, (position, deferred) in enumerate(waiting_list):
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if position <= token:
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try:
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with PreserveLoggingContext():
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deferred.callback(None)
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except Exception:
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# The deferred has been cancelled or timed out.
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pass
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else:
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# The list is sorted by position so we don't need to continue
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# checking any futher entries in the list.
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index_of_first_deferred_not_called = idx
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break
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# Drop all entries in the waiting list that were called in the above
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# loop. (This maintains the order so no need to resort)
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waiting_list[:] = waiting_list[index_of_first_deferred_not_called:]
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async def on_position(self, stream_name: str, instance_name: str, token: int):
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self.store.process_replication_rows(stream_name, instance_name, token, [])
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def on_remote_server_up(self, server: str):
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"""Called when get a new REMOTE_SERVER_UP command."""
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async def wait_for_stream_position(
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self, instance_name: str, stream_name: str, position: int
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):
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"""Wait until this instance has received updates up to and including
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the given stream position.
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"""
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if instance_name == self._instance_name:
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# We don't get told about updates written by this process, and
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# anyway in that case we don't need to wait.
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return
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current_position = self._streams[stream_name].current_token(self._instance_name)
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if position <= current_position:
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# We're already past the position
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return
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# Create a new deferred that times out after N seconds, as we don't want
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# to wedge here forever.
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deferred = Deferred()
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deferred = timeout_deferred(
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deferred, _WAIT_FOR_REPLICATION_TIMEOUT_SECONDS, self._reactor
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)
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waiting_list = self._streams_to_waiters.setdefault(stream_name, [])
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# We insert into the list using heapq as it is more efficient than
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# pushing then resorting each time.
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heapq.heappush(waiting_list, (position, deferred))
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# We measure here to get in flight counts and average waiting time.
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with Measure(self._clock, "repl.wait_for_stream_position"):
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logger.info("Waiting for repl stream %r to reach %s", stream_name, position)
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await make_deferred_yieldable(deferred)
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logger.info(
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"Finished waiting for repl stream %r to reach %s", stream_name, position
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)
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