forked-synapse/synapse/replication/tcp/streams/events.py
Erik Johnston 8f35f8148e
Fix bug where a new writer advances their token too quickly (#16473)
* Fix bug where a new writer advances their token too quickly

When starting a new writer (for e.g. persisting events), the
`MultiWriterIdGenerator` doesn't have a minimum token for it as there
are no rows matching that new writer in the DB.

This results in the the first stream ID it acquired being announced as
persisted *before* it actually finishes persisting, if another writer
gets and persists a subsequent stream ID. This is due to the logic of
setting the minimum persisted position to the minimum known position of
across all writers, and the new writer starts off not being considered.

* Fix sending out POSITIONs when our token advances without update

Broke in #14820

* For replication HTTP requests, only wait for minimal position
2023-10-23 16:57:30 +01:00

276 lines
9.5 KiB
Python

# Copyright 2017 Vector Creations Ltd
# Copyright 2019 New Vector Ltd
#
# 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 heapq
from collections import defaultdict
from typing import TYPE_CHECKING, Iterable, Optional, Tuple, Type, TypeVar, cast
import attr
from synapse.replication.tcp.streams._base import (
StreamRow,
StreamUpdateResult,
Token,
_StreamFromIdGen,
)
if TYPE_CHECKING:
from synapse.server import HomeServer
"""Handling of the 'events' replication stream
This stream contains rows of various types. Each row therefore contains a 'type'
identifier before the real data. For example::
RDATA events batch ["state", ["!room:id", "m.type", "", "$event:id"]]
RDATA events 12345 ["ev", ["$event:id", "!room:id", "m.type", null, null]]
An "ev" row is sent for each new event. The fields in the data part are:
* The new event id
* The room id for the event
* The type of the new event
* The state key of the event, for state events
* The event id of an event which is redacted by this event.
A "state" row is sent whenever the "current state" in a room changes. The fields in the
data part are:
* The room id for the state change
* The event type of the state which has changed
* The state_key of the state which has changed
* The event id of the new state
A "state-all" row is sent whenever the "current state" in a room changes, but there are
too many state updates for a particular room in the same update. This replaces any
"state" rows on a per-room basis. The fields in the data part are:
* The room id for the state changes
"""
# Any room with more than _MAX_STATE_UPDATES_PER_ROOM will send a EventsStreamAllStateRow
# instead of individual EventsStreamEventRow. This is predominantly useful when
# purging large rooms.
_MAX_STATE_UPDATES_PER_ROOM = 150
@attr.s(slots=True, frozen=True, auto_attribs=True)
class EventsStreamRow:
"""A parsed row from the events replication stream"""
type: str # the TypeId of one of the *EventsStreamRows
data: "BaseEventsStreamRow"
T = TypeVar("T", bound="BaseEventsStreamRow")
class BaseEventsStreamRow:
"""Base class for rows to be sent in the events stream.
Specifies how to identify, serialize and deserialize the different types.
"""
# Unique string that ids the type. Must be overridden in sub classes.
TypeId: str
@classmethod
def from_data(cls: Type[T], data: Iterable[Optional[str]]) -> T:
"""Parse the data from the replication stream into a row.
By default we just call the constructor with the data list as arguments
Args:
data: The value of the data object from the replication stream
"""
return cls(*data)
@attr.s(slots=True, frozen=True, auto_attribs=True)
class EventsStreamEventRow(BaseEventsStreamRow):
TypeId = "ev"
event_id: str
room_id: str
type: str
state_key: Optional[str]
redacts: Optional[str]
relates_to: Optional[str]
membership: Optional[str]
rejected: bool
outlier: bool
@attr.s(slots=True, frozen=True, auto_attribs=True)
class EventsStreamCurrentStateRow(BaseEventsStreamRow):
TypeId = "state"
room_id: str
type: str
state_key: str
event_id: Optional[str]
@attr.s(slots=True, frozen=True, auto_attribs=True)
class EventsStreamAllStateRow(BaseEventsStreamRow):
TypeId = "state-all"
room_id: str
_EventRows: Tuple[Type[BaseEventsStreamRow], ...] = (
EventsStreamEventRow,
EventsStreamCurrentStateRow,
EventsStreamAllStateRow,
)
TypeToRow = {Row.TypeId: Row for Row in _EventRows}
class EventsStream(_StreamFromIdGen):
"""We received a new event, or an event went from being an outlier to not"""
NAME = "events"
def __init__(self, hs: "HomeServer"):
self._store = hs.get_datastores().main
super().__init__(
hs.get_instance_name(), self._update_function, self._store._stream_id_gen
)
async def _update_function(
self,
instance_name: str,
from_token: Token,
current_token: Token,
target_row_count: int,
) -> StreamUpdateResult:
# the events stream merges together three separate sources:
# * new events
# * current_state changes
# * events which were previously outliers, but have now been de-outliered.
#
# The merge operation is complicated by the fact that we only have a single
# "stream token" which is supposed to indicate how far we have got through
# all three streams. It's therefore no good to return rows 1-1000 from the
# "new events" table if the state_deltas are limited to rows 1-100 by the
# target_row_count.
#
# In other words: we must pick a new upper limit, and must return *all* rows
# up to that point for each of the three sources.
#
# Start by trying to split the target_row_count up. We expect to have a
# negligible number of ex-outliers, and a rough approximation based on recent
# traffic on sw1v.org shows that there are approximately the same number of
# event rows between a given pair of stream ids as there are state
# updates, so let's split our target_row_count among those two types. The target
# is only an approximation - it doesn't matter if we end up going a bit over it.
target_row_count //= 2
# now we fetch up to that many rows from the events table
event_rows = await self._store.get_all_new_forward_event_rows(
instance_name, from_token, current_token, target_row_count
)
# we rely on get_all_new_forward_event_rows strictly honouring the limit, so
# that we know it is safe to just take upper_limit = event_rows[-1][0].
assert (
len(event_rows) <= target_row_count
), "get_all_new_forward_event_rows did not honour row limit"
# if we hit the limit on event_updates, there's no point in going beyond the
# last stream_id in the batch for the other sources.
if len(event_rows) == target_row_count:
limited = True
upper_limit: int = event_rows[-1][0]
else:
limited = False
upper_limit = current_token
# next up is the state delta table.
(
state_rows,
upper_limit,
state_rows_limited,
) = await self._store.get_all_updated_current_state_deltas(
instance_name, from_token, upper_limit, target_row_count
)
limited = limited or state_rows_limited
# finally, fetch the ex-outliers rows. We assume there are few enough of these
# not to bother with the limit.
ex_outliers_rows = await self._store.get_ex_outlier_stream_rows(
instance_name, from_token, upper_limit
)
# we now need to turn the raw database rows returned into tuples suitable
# for the replication protocol (basically, we add an identifier to
# distinguish the row type). At the same time, we can limit the event_rows
# to the max stream_id from state_rows.
event_updates: Iterable[Tuple[int, Tuple]] = (
(stream_id, (EventsStreamEventRow.TypeId, rest))
for (stream_id, *rest) in event_rows
if stream_id <= upper_limit
)
# Separate out rooms that have many state updates, listeners should clear
# all state for those rooms.
state_updates_by_room = defaultdict(list)
for stream_id, room_id, _type, _state_key, _event_id in state_rows:
state_updates_by_room[room_id].append(stream_id)
state_all_rows = [
(stream_ids[-1], room_id)
for room_id, stream_ids in state_updates_by_room.items()
if len(stream_ids) >= _MAX_STATE_UPDATES_PER_ROOM
]
state_all_updates: Iterable[Tuple[int, Tuple]] = (
(max_stream_id, (EventsStreamAllStateRow.TypeId, (room_id,)))
for (max_stream_id, room_id) in state_all_rows
)
# Any remaining state updates are sent individually.
state_all_rooms = {room_id for _, room_id in state_all_rows}
state_updates: Iterable[Tuple[int, Tuple]] = (
(stream_id, (EventsStreamCurrentStateRow.TypeId, rest))
for (stream_id, *rest) in state_rows
if rest[0] not in state_all_rooms
)
ex_outliers_updates: Iterable[Tuple[int, Tuple]] = (
(stream_id, (EventsStreamEventRow.TypeId, rest))
for (stream_id, *rest) in ex_outliers_rows
)
# we need to return a sorted list, so merge them together.
updates = list(
heapq.merge(
event_updates, state_all_updates, state_updates, ex_outliers_updates
)
)
return updates, upper_limit, limited
@classmethod
def parse_row(cls, row: StreamRow) -> "EventsStreamRow":
(typ, data) = cast(Tuple[str, Iterable[Optional[str]]], row)
event_stream_row_data = TypeToRow[typ].from_data(data)
return EventsStreamRow(typ, event_stream_row_data)