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Optimise queueing of inbound replication commands (#7861)
When we get behind on replication, we tend to stack up background processes behind a linearizer. Bg processes are heavy (particularly with respect to prometheus metrics) and linearizers aren't terribly efficient once the queue gets long either. A better approach is to maintain a queue of requests to be processed, and nominate a single process to work its way through the queue. Fixes: #7444
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changelog.d/7861.misc
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changelog.d/7861.misc
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Optimise queueing of inbound replication commands.
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@ -14,9 +14,21 @@
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# See the License for the specific language governing permissions and
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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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# limitations under the License.
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import logging
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import logging
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from typing import Any, Dict, Iterable, Iterator, List, Optional, Set, Tuple, TypeVar
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from typing import (
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Any,
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Dict,
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Iterable,
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Iterator,
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List,
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Optional,
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Set,
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Tuple,
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TypeVar,
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Union,
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)
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from prometheus_client import Counter
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from prometheus_client import Counter
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from typing_extensions import Deque
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from twisted.internet.protocol import ReconnectingClientFactory
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from twisted.internet.protocol import ReconnectingClientFactory
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@ -44,7 +56,6 @@ from synapse.replication.tcp.streams import (
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Stream,
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Stream,
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TypingStream,
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TypingStream,
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)
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)
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from synapse.util.async_helpers import Linearizer
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logger = logging.getLogger(__name__)
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logger = logging.getLogger(__name__)
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@ -62,6 +73,12 @@ invalidate_cache_counter = Counter(
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user_ip_cache_counter = Counter("synapse_replication_tcp_resource_user_ip_cache", "")
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user_ip_cache_counter = Counter("synapse_replication_tcp_resource_user_ip_cache", "")
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# the type of the entries in _command_queues_by_stream
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_StreamCommandQueue = Deque[
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Tuple[Union[RdataCommand, PositionCommand], AbstractConnection]
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]
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class ReplicationCommandHandler:
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class ReplicationCommandHandler:
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"""Handles incoming commands from replication as well as sending commands
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"""Handles incoming commands from replication as well as sending commands
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back out to connections.
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back out to connections.
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@ -116,10 +133,6 @@ class ReplicationCommandHandler:
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self._streams_to_replicate.append(stream)
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self._streams_to_replicate.append(stream)
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self._position_linearizer = Linearizer(
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"replication_position", clock=self._clock
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)
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# Map of stream name to batched updates. See RdataCommand for info on
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# Map of stream name to batched updates. See RdataCommand for info on
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# how batching works.
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# how batching works.
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self._pending_batches = {} # type: Dict[str, List[Any]]
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self._pending_batches = {} # type: Dict[str, List[Any]]
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@ -131,10 +144,6 @@ class ReplicationCommandHandler:
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# outgoing replication commands to.)
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# outgoing replication commands to.)
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self._connections = [] # type: List[AbstractConnection]
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self._connections = [] # type: List[AbstractConnection]
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# For each connection, the incoming stream names that are coming from
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# that connection.
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self._streams_by_connection = {} # type: Dict[AbstractConnection, Set[str]]
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LaterGauge(
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LaterGauge(
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"synapse_replication_tcp_resource_total_connections",
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"synapse_replication_tcp_resource_total_connections",
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"",
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"",
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@ -142,6 +151,32 @@ class ReplicationCommandHandler:
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lambda: len(self._connections),
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lambda: len(self._connections),
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)
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)
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# When POSITION or RDATA commands arrive, we stick them in a queue and process
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# them in order in a separate background process.
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# the streams which are currently being processed by _unsafe_process_stream
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self._processing_streams = set() # type: Set[str]
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# for each stream, a queue of commands that are awaiting processing, and the
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# connection that they arrived on.
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self._command_queues_by_stream = {
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stream_name: _StreamCommandQueue() for stream_name in self._streams
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}
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# For each connection, the incoming stream names that have received a POSITION
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# from that connection.
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self._streams_by_connection = {} # type: Dict[AbstractConnection, Set[str]]
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LaterGauge(
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"synapse_replication_tcp_command_queue",
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"Number of inbound RDATA/POSITION commands queued for processing",
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["stream_name"],
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lambda: {
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(stream_name,): len(queue)
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for stream_name, queue in self._command_queues_by_stream.items()
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},
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)
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self._is_master = hs.config.worker_app is None
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self._is_master = hs.config.worker_app is None
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self._federation_sender = None
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self._federation_sender = None
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@ -152,6 +187,64 @@ class ReplicationCommandHandler:
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if self._is_master:
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if self._is_master:
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self._server_notices_sender = hs.get_server_notices_sender()
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self._server_notices_sender = hs.get_server_notices_sender()
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async def _add_command_to_stream_queue(
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self, conn: AbstractConnection, cmd: Union[RdataCommand, PositionCommand]
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) -> None:
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"""Queue the given received command for processing
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Adds the given command to the per-stream queue, and processes the queue if
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necessary
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"""
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stream_name = cmd.stream_name
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queue = self._command_queues_by_stream.get(stream_name)
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if queue is None:
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logger.error("Got %s for unknown stream: %s", cmd.NAME, stream_name)
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return
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# if we're already processing this stream, stick the new command in the
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# queue, and we're done.
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if stream_name in self._processing_streams:
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queue.append((cmd, conn))
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return
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# otherwise, process the new command.
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# arguably we should start off a new background process here, but nothing
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# will be too upset if we don't return for ages, so let's save the overhead
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# and use the existing logcontext.
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self._processing_streams.add(stream_name)
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try:
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# might as well skip the queue for this one, since it must be empty
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assert not queue
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await self._process_command(cmd, conn, stream_name)
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# now process any other commands that have built up while we were
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# dealing with that one.
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while queue:
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cmd, conn = queue.popleft()
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try:
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await self._process_command(cmd, conn, stream_name)
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except Exception:
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logger.exception("Failed to handle command %s", cmd)
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finally:
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self._processing_streams.discard(stream_name)
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async def _process_command(
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self,
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cmd: Union[PositionCommand, RdataCommand],
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conn: AbstractConnection,
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stream_name: str,
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) -> None:
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if isinstance(cmd, PositionCommand):
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await self._process_position(stream_name, conn, cmd)
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elif isinstance(cmd, RdataCommand):
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await self._process_rdata(stream_name, conn, cmd)
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else:
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# This shouldn't be possible
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raise Exception("Unrecognised command %s in stream queue", cmd.NAME)
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def start_replication(self, hs):
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def start_replication(self, hs):
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"""Helper method to start a replication connection to the remote server
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"""Helper method to start a replication connection to the remote server
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using TCP.
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using TCP.
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@ -285,18 +378,28 @@ class ReplicationCommandHandler:
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stream_name = cmd.stream_name
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stream_name = cmd.stream_name
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inbound_rdata_count.labels(stream_name).inc()
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inbound_rdata_count.labels(stream_name).inc()
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try:
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# We put the received command into a queue here for two reasons:
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row = STREAMS_MAP[stream_name].parse_row(cmd.row)
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except Exception:
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logger.exception("Failed to parse RDATA: %r %r", stream_name, cmd.row)
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raise
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# We linearize here for two reasons:
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# 1. so we don't try and concurrently handle multiple rows for the
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# 1. so we don't try and concurrently handle multiple rows for the
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# same stream, and
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# same stream, and
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# 2. so we don't race with getting a POSITION command and fetching
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# 2. so we don't race with getting a POSITION command and fetching
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# missing RDATA.
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# missing RDATA.
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with await self._position_linearizer.queue(cmd.stream_name):
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await self._add_command_to_stream_queue(conn, cmd)
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async def _process_rdata(
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self, stream_name: str, conn: AbstractConnection, cmd: RdataCommand
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) -> None:
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"""Process an RDATA command
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Called after the command has been popped off the queue of inbound commands
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"""
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try:
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row = STREAMS_MAP[stream_name].parse_row(cmd.row)
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except Exception as e:
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raise Exception(
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"Failed to parse RDATA: %r %r" % (stream_name, cmd.row)
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) from e
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# make sure that we've processed a POSITION for this stream *on this
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# make sure that we've processed a POSITION for this stream *on this
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# connection*. (A POSITION on another connection is no good, as there
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# connection*. (A POSITION on another connection is no good, as there
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# is no guarantee that we have seen all the intermediate updates.)
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# is no guarantee that we have seen all the intermediate updates.)
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@ -316,15 +419,13 @@ class ReplicationCommandHandler:
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# which case batch until we get an update for the stream with a non
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# which case batch until we get an update for the stream with a non
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# None token).
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# None token).
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self._pending_batches.setdefault(stream_name, []).append(row)
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self._pending_batches.setdefault(stream_name, []).append(row)
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else:
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return
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# Check if this is the last of a batch of updates
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# Check if this is the last of a batch of updates
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rows = self._pending_batches.pop(stream_name, [])
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rows = self._pending_batches.pop(stream_name, [])
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rows.append(row)
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rows.append(row)
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stream = self._streams.get(stream_name)
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stream = self._streams[stream_name]
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if not stream:
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logger.error("Got RDATA for unknown stream: %s", stream_name)
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return
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# Find where we previously streamed up to.
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# Find where we previously streamed up to.
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current_token = stream.current_token(cmd.instance_name)
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current_token = stream.current_token(cmd.instance_name)
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@ -367,15 +468,17 @@ class ReplicationCommandHandler:
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logger.info("Handling '%s %s'", cmd.NAME, cmd.to_line())
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logger.info("Handling '%s %s'", cmd.NAME, cmd.to_line())
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stream_name = cmd.stream_name
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await self._add_command_to_stream_queue(conn, cmd)
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stream = self._streams.get(stream_name)
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if not stream:
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async def _process_position(
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logger.error("Got POSITION for unknown stream: %s", stream_name)
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self, stream_name: str, conn: AbstractConnection, cmd: PositionCommand
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return
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) -> None:
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"""Process a POSITION command
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Called after the command has been popped off the queue of inbound commands
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"""
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stream = self._streams[stream_name]
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# We protect catching up with a linearizer in case the replication
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# connection reconnects under us.
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with await self._position_linearizer.queue(stream_name):
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# We're about to go and catch up with the stream, so remove from set
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# We're about to go and catch up with the stream, so remove from set
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# of connected streams.
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# of connected streams.
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for streams in self._streams_by_connection.values():
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for streams in self._streams_by_connection.values():
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@ -399,11 +502,7 @@ class ReplicationCommandHandler:
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current_token,
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current_token,
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cmd.token,
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cmd.token,
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)
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)
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(
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(updates, current_token, missing_updates) = await stream.get_updates_since(
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updates,
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current_token,
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missing_updates,
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) = await stream.get_updates_since(
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cmd.instance_name, current_token, cmd.token
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cmd.instance_name, current_token, cmd.token
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)
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)
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