Optimise backfill calculation (#12522)
Try to avoid an OOM by checking fewer extremities. Generally this is a big rewrite of _maybe_backfill, to try and fix some of the TODOs and other problems in it. It's best reviewed commit-by-commit.pull/12564/head
Richard van der Hoff
GitHub
parent
e75c7e3b6d
commit
17d99f758a
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@ -0,0 +1 @@
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Fix a bug introduced in Synapse 0.99.3 which could cause Synapse to consume large amounts of RAM when back-paginating in a large room.
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@ -1,4 +1,4 @@
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# Copyright 2014-2021 The Matrix.org Foundation C.I.C.
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# Copyright 2014-2022 The Matrix.org Foundation C.I.C.
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# Copyright 2020 Sorunome
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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@ -15,10 +15,14 @@
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"""Contains handlers for federation events."""
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import enum
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import itertools
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import logging
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from enum import Enum
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from http import HTTPStatus
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from typing import TYPE_CHECKING, Dict, Iterable, List, Optional, Tuple, Union
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import attr
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from signedjson.key import decode_verify_key_bytes
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from signedjson.sign import verify_signed_json
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from unpaddedbase64 import decode_base64
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@ -92,6 +96,24 @@ def get_domains_from_state(state: StateMap[EventBase]) -> List[Tuple[str, int]]:
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return sorted(joined_domains.items(), key=lambda d: d[1])
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class _BackfillPointType(Enum):
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# a regular backwards extremity (ie, an event which we don't yet have, but which
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# is referred to by other events in the DAG)
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BACKWARDS_EXTREMITY = enum.auto()
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# an MSC2716 "insertion event"
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INSERTION_PONT = enum.auto()
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@attr.s(slots=True, auto_attribs=True, frozen=True)
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class _BackfillPoint:
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"""A potential point we might backfill from"""
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event_id: str
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depth: int
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type: _BackfillPointType
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class FederationHandler:
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"""Handles general incoming federation requests
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@ -157,89 +179,51 @@ class FederationHandler:
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async def _maybe_backfill_inner(
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self, room_id: str, current_depth: int, limit: int
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) -> bool:
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oldest_events_with_depth = (
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await self.store.get_oldest_event_ids_with_depth_in_room(room_id)
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)
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backwards_extremities = [
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_BackfillPoint(event_id, depth, _BackfillPointType.BACKWARDS_EXTREMITY)
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for event_id, depth in await self.store.get_oldest_event_ids_with_depth_in_room(
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room_id
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)
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]
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insertion_events_to_be_backfilled: Dict[str, int] = {}
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insertion_events_to_be_backfilled: List[_BackfillPoint] = []
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if self.hs.config.experimental.msc2716_enabled:
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insertion_events_to_be_backfilled = (
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await self.store.get_insertion_event_backward_extremities_in_room(
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insertion_events_to_be_backfilled = [
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_BackfillPoint(event_id, depth, _BackfillPointType.INSERTION_PONT)
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for event_id, depth in await self.store.get_insertion_event_backward_extremities_in_room(
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room_id
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)
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)
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]
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logger.debug(
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"_maybe_backfill_inner: extremities oldest_events_with_depth=%s insertion_events_to_be_backfilled=%s",
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oldest_events_with_depth,
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"_maybe_backfill_inner: backwards_extremities=%s insertion_events_to_be_backfilled=%s",
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backwards_extremities,
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insertion_events_to_be_backfilled,
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)
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if not oldest_events_with_depth and not insertion_events_to_be_backfilled:
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if not backwards_extremities and not insertion_events_to_be_backfilled:
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logger.debug("Not backfilling as no extremeties found.")
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return False
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# We only want to paginate if we can actually see the events we'll get,
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# as otherwise we'll just spend a lot of resources to get redacted
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# events.
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#
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# We do this by filtering all the backwards extremities and seeing if
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# any remain. Given we don't have the extremity events themselves, we
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# need to actually check the events that reference them.
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#
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# *Note*: the spec wants us to keep backfilling until we reach the start
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# of the room in case we are allowed to see some of the history. However
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# in practice that causes more issues than its worth, as a) its
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# relatively rare for there to be any visible history and b) even when
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# there is its often sufficiently long ago that clients would stop
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# attempting to paginate before backfill reached the visible history.
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#
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# TODO: If we do do a backfill then we should filter the backwards
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# extremities to only include those that point to visible portions of
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# history.
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#
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# TODO: Correctly handle the case where we are allowed to see the
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# forward event but not the backward extremity, e.g. in the case of
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# initial join of the server where we are allowed to see the join
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# event but not anything before it. This would require looking at the
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# state *before* the event, ignoring the special casing certain event
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# types have.
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forward_event_ids = await self.store.get_successor_events(
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list(oldest_events_with_depth)
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# we now have a list of potential places to backpaginate from. We prefer to
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# start with the most recent (ie, max depth), so let's sort the list.
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sorted_backfill_points: List[_BackfillPoint] = sorted(
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itertools.chain(
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backwards_extremities,
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insertion_events_to_be_backfilled,
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),
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key=lambda e: -int(e.depth),
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)
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extremities_events = await self.store.get_events(
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forward_event_ids,
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redact_behaviour=EventRedactBehaviour.AS_IS,
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get_prev_content=False,
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)
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# We set `check_history_visibility_only` as we might otherwise get false
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# positives from users having been erased.
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filtered_extremities = await filter_events_for_server(
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self.storage,
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self.server_name,
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list(extremities_events.values()),
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redact=False,
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check_history_visibility_only=True,
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)
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logger.debug(
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"_maybe_backfill_inner: filtered_extremities %s", filtered_extremities
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"_maybe_backfill_inner: room_id: %s: current_depth: %s, limit: %s, "
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"backfill points (%d): %s",
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room_id,
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current_depth,
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limit,
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len(sorted_backfill_points),
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sorted_backfill_points,
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)
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if not filtered_extremities and not insertion_events_to_be_backfilled:
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return False
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extremities = {
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**oldest_events_with_depth,
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# TODO: insertion_events_to_be_backfilled is currently skipping the filtered_extremities checks
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**insertion_events_to_be_backfilled,
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}
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# Check if we reached a point where we should start backfilling.
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sorted_extremeties_tuple = sorted(extremities.items(), key=lambda e: -int(e[1]))
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max_depth = sorted_extremeties_tuple[0][1]
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# If we're approaching an extremity we trigger a backfill, otherwise we
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# no-op.
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#
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@ -249,6 +233,11 @@ class FederationHandler:
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# chose more than one times the limit in case of failure, but choosing a
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# much larger factor will result in triggering a backfill request much
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# earlier than necessary.
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#
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# XXX: shouldn't we do this *after* the filter by depth below? Again, we don't
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# care about events that have happened after our current position.
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#
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max_depth = sorted_backfill_points[0].depth
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if current_depth - 2 * limit > max_depth:
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logger.debug(
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"Not backfilling as we don't need to. %d < %d - 2 * %d",
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@ -265,31 +254,98 @@ class FederationHandler:
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# 2. we have likely previously tried and failed to backfill from that
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# extremity, so to avoid getting "stuck" requesting the same
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# backfill repeatedly we drop those extremities.
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filtered_sorted_extremeties_tuple = [
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t for t in sorted_extremeties_tuple if int(t[1]) <= current_depth
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]
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logger.debug(
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"room_id: %s, backfill: current_depth: %s, limit: %s, max_depth: %s, extrems (%d): %s filtered_sorted_extremeties_tuple: %s",
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room_id,
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current_depth,
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limit,
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max_depth,
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len(sorted_extremeties_tuple),
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sorted_extremeties_tuple,
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filtered_sorted_extremeties_tuple,
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)
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#
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# However, we need to check that the filtered extremities are non-empty.
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# If they are empty then either we can a) bail or b) still attempt to
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# backfill. We opt to try backfilling anyway just in case we do get
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# relevant events.
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if filtered_sorted_extremeties_tuple:
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sorted_extremeties_tuple = filtered_sorted_extremeties_tuple
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#
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filtered_sorted_backfill_points = [
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t for t in sorted_backfill_points if t.depth <= current_depth
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]
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if filtered_sorted_backfill_points:
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logger.debug(
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"_maybe_backfill_inner: backfill points before current depth: %s",
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filtered_sorted_backfill_points,
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)
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sorted_backfill_points = filtered_sorted_backfill_points
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else:
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logger.debug(
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"_maybe_backfill_inner: all backfill points are *after* current depth. Backfilling anyway."
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)
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# We don't want to specify too many extremities as it causes the backfill
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# request URI to be too long.
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extremities = dict(sorted_extremeties_tuple[:5])
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# For performance's sake, we only want to paginate from a particular extremity
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# if we can actually see the events we'll get. Otherwise, we'd just spend a lot
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# of resources to get redacted events. We check each extremity in turn and
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# ignore those which users on our server wouldn't be able to see.
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#
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# Additionally, we limit ourselves to backfilling from at most 5 extremities,
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# for two reasons:
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#
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# - The check which determines if we can see an extremity's events can be
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# expensive (we load the full state for the room at each of the backfill
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# points, or (worse) their successors)
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# - We want to avoid the server-server API request URI becoming too long.
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#
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# *Note*: the spec wants us to keep backfilling until we reach the start
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# of the room in case we are allowed to see some of the history. However,
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# in practice that causes more issues than its worth, as (a) it's
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# relatively rare for there to be any visible history and (b) even when
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# there is it's often sufficiently long ago that clients would stop
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# attempting to paginate before backfill reached the visible history.
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extremities_to_request: List[str] = []
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for bp in sorted_backfill_points:
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if len(extremities_to_request) >= 5:
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break
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# For regular backwards extremities, we don't have the extremity events
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# themselves, so we need to actually check the events that reference them -
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# their "successor" events.
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#
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# TODO: Correctly handle the case where we are allowed to see the
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# successor event but not the backward extremity, e.g. in the case of
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# initial join of the server where we are allowed to see the join
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# event but not anything before it. This would require looking at the
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# state *before* the event, ignoring the special casing certain event
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# types have.
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if bp.type == _BackfillPointType.INSERTION_PONT:
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event_ids_to_check = [bp.event_id]
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else:
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event_ids_to_check = await self.store.get_successor_events(bp.event_id)
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events_to_check = await self.store.get_events_as_list(
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event_ids_to_check,
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redact_behaviour=EventRedactBehaviour.AS_IS,
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get_prev_content=False,
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)
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# We set `check_history_visibility_only` as we might otherwise get false
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# positives from users having been erased.
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filtered_extremities = await filter_events_for_server(
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self.storage,
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self.server_name,
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events_to_check,
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redact=False,
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check_history_visibility_only=True,
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)
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if filtered_extremities:
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extremities_to_request.append(bp.event_id)
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else:
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logger.debug(
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"_maybe_backfill_inner: skipping extremity %s as it would not be visible",
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bp,
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)
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if not extremities_to_request:
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logger.debug(
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"_maybe_backfill_inner: found no extremities which would be visible"
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)
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return False
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logger.debug(
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"_maybe_backfill_inner: extremities_to_request %s", extremities_to_request
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)
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# Now we need to decide which hosts to hit first.
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@ -309,7 +365,7 @@ class FederationHandler:
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for dom in domains:
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try:
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await self._federation_event_handler.backfill(
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dom, room_id, limit=100, extremities=extremities
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dom, room_id, limit=100, extremities=extremities_to_request
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)
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# If this succeeded then we probably already have the
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# appropriate stuff.
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@ -54,7 +54,7 @@ class RoomBatchHandler:
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# it has a larger `depth` but before the successor event because the `stream_ordering`
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# is negative before the successor event.
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successor_event_ids = await self.store.get_successor_events(
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[most_recent_prev_event_id]
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most_recent_prev_event_id
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)
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# If we can't find any successor events, then it's a forward extremity of
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@ -695,7 +695,9 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
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# Return all events where not all sets can reach them.
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return {eid for eid, n in event_to_missing_sets.items() if n}
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async def get_oldest_event_ids_with_depth_in_room(self, room_id) -> Dict[str, int]:
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async def get_oldest_event_ids_with_depth_in_room(
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self, room_id
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) -> List[Tuple[str, int]]:
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"""Gets the oldest events(backwards extremities) in the room along with the
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aproximate depth.
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@ -708,7 +710,7 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
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room_id: Room where we want to find the oldest events
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Returns:
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Map from event_id to depth
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List of (event_id, depth) tuples
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"""
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def get_oldest_event_ids_with_depth_in_room_txn(txn, room_id):
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@ -741,7 +743,7 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
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txn.execute(sql, (room_id, False))
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return dict(txn)
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return txn.fetchall()
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return await self.db_pool.runInteraction(
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"get_oldest_event_ids_with_depth_in_room",
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@ -751,7 +753,7 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
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async def get_insertion_event_backward_extremities_in_room(
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self, room_id
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) -> Dict[str, int]:
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) -> List[Tuple[str, int]]:
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"""Get the insertion events we know about that we haven't backfilled yet.
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We use this function so that we can compare and see if someones current
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@ -763,7 +765,7 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
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room_id: Room where we want to find the oldest events
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Returns:
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Map from event_id to depth
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List of (event_id, depth) tuples
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"""
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def get_insertion_event_backward_extremities_in_room_txn(txn, room_id):
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@ -778,8 +780,7 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
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"""
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txn.execute(sql, (room_id,))
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return dict(txn)
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return txn.fetchall()
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return await self.db_pool.runInteraction(
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"get_insertion_event_backward_extremities_in_room",
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@ -1295,22 +1296,19 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
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event_results.reverse()
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return event_results
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async def get_successor_events(self, event_ids: Iterable[str]) -> List[str]:
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"""Fetch all events that have the given events as a prev event
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async def get_successor_events(self, event_id: str) -> List[str]:
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"""Fetch all events that have the given event as a prev event
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Args:
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event_ids: The events to use as the previous events.
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event_id: The event to search for as a prev_event.
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"""
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rows = await self.db_pool.simple_select_many_batch(
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return await self.db_pool.simple_select_onecol(
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table="event_edges",
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column="prev_event_id",
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iterable=event_ids,
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retcols=("event_id",),
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keyvalues={"prev_event_id": event_id},
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retcol="event_id",
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desc="get_successor_events",
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)
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return [row["event_id"] for row in rows]
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@wrap_as_background_process("delete_old_forward_extrem_cache")
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async def _delete_old_forward_extrem_cache(self) -> None:
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def _delete_old_forward_extrem_cache_txn(txn):
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|
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@ -419,6 +419,13 @@ async def _event_to_memberships(
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return {}
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# for each event, get the event_ids of the membership state at those events.
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#
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# TODO: this means that we request the entire membership list. If there are only
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# one or two users on this server, and the room is huge, this is very wasteful
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# (it means more db work, and churns the *stateGroupMembersCache*).
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# It might be that we could extend StateFilter to specify "give me keys matching
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# *:<server_name>", to avoid this.
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event_to_state_ids = await storage.state.get_state_ids_for_events(
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frozenset(e.event_id for e in events),
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state_filter=StateFilter.from_types(types=((EventTypes.Member, None),)),
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