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Try and drop stale extremities. (#8929)

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If we see stale extremities while persisting events, and notice that
they don't change the result of state resolution, we drop them.
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Erik Johnston 2020-12-18 09:49:18 +00:00 • committed by GitHub
parent f1db20b5a5
commit 70586aa63e
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6 changed files with 523 additions and 18 deletions
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200
synapse/storage/persist_events.py
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@ -31,7 +31,14 @@ from synapse.logging.context import PreserveLoggingContext, make_deferred_yielda
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.storage.databases import Databases
from synapse.storage.databases.main.events import DeltaState
from synapse.types import Collection, PersistedEventPosition, RoomStreamToken, StateMap
from synapse.storage.databases.main.events_worker import EventRedactBehaviour
from synapse.types import (
Collection,
PersistedEventPosition,
RoomStreamToken,
StateMap,
get_domain_from_id,
)
from synapse.util.async_helpers import ObservableDeferred
from synapse.util.metrics import Measure
@ -68,6 +75,21 @@ stale_forward_extremities_counter = Histogram(
buckets=(0, 1, 2, 3, 5, 7, 10, 15, 20, 50, 100, 200, 500, "+Inf"),
)
state_resolutions_during_persistence = Counter(
"synapse_storage_events_state_resolutions_during_persistence",
"Number of times we had to do state res to calculate new current state",
)
potential_times_prune_extremities = Counter(
"synapse_storage_events_potential_times_prune_extremities",
"Number of times we might be able to prune extremities",
)
times_pruned_extremities = Counter(
"synapse_storage_events_times_pruned_extremities",
"Number of times we were actually be able to prune extremities",
)
class _EventPeristenceQueue:
"""Queues up events so that they can be persisted in bulk with only one
@ -454,7 +476,15 @@ class EventsPersistenceStorage:
latest_event_ids,
new_latest_event_ids,
)
current_state, delta_ids = res
current_state, delta_ids, new_latest_event_ids = res
# there should always be at least one forward extremity.
# (except during the initial persistence of the send_join
# results, in which case there will be no existing
# extremities, so we'll `continue` above and skip this bit.)
assert new_latest_event_ids, "No forward extremities left!"
new_forward_extremeties[room_id] = new_latest_event_ids
# If either are not None then there has been a change,
# and we need to work out the delta (or use that
@ -573,29 +603,35 @@ class EventsPersistenceStorage:
self,
room_id: str,
events_context: List[Tuple[EventBase, EventContext]],
old_latest_event_ids: Iterable[str],
new_latest_event_ids: Iterable[str],
) -> Tuple[Optional[StateMap[str]], Optional[StateMap[str]]]:
old_latest_event_ids: Set[str],
new_latest_event_ids: Set[str],
) -> Tuple[Optional[StateMap[str]], Optional[StateMap[str]], Set[str]]:
"""Calculate the current state dict after adding some new events to
a room
Args:
room_id (str):
room_id:
room to which the events are being added. Used for logging etc
events_context (list[(EventBase, EventContext)]):
events_context:
events and contexts which are being added to the room
old_latest_event_ids (iterable[str]):
old_latest_event_ids:
the old forward extremities for the room.
new_latest_event_ids (iterable[str]):
new_latest_event_ids :
the new forward extremities for the room.
Returns:
Returns a tuple of two state maps, the first being the full new current
state and the second being the delta to the existing current state.
If both are None then there has been no change.
Returns a tuple of two state maps and a set of new forward
extremities.
The first state map is the full new current state and the second
is the delta to the existing current state. If both are None then
there has been no change.
The function may prune some old entries from the set of new
forward extremities if it's safe to do so.
If there has been a change then we only return the delta if its
already been calculated. Conversely if we do know the delta then
@ -672,7 +708,7 @@ class EventsPersistenceStorage:
# If they old and new groups are the same then we don't need to do
# anything.
if old_state_groups == new_state_groups:
return None, None
return None, None, new_latest_event_ids
if len(new_state_groups) == 1 and len(old_state_groups) == 1:
# If we're going from one state group to another, lets check if
@ -689,7 +725,7 @@ class EventsPersistenceStorage:
# the current state in memory then lets also return that,
# but it doesn't matter if we don't.
new_state = state_groups_map.get(new_state_group)
return new_state, delta_ids
return new_state, delta_ids, new_latest_event_ids
# Now that we have calculated new_state_groups we need to get
# their state IDs so we can resolve to a single state set.
@ -701,7 +737,7 @@ class EventsPersistenceStorage:
if len(new_state_groups) == 1:
# If there is only one state group, then we know what the current
# state is.
return state_groups_map[new_state_groups.pop()], None
return state_groups_map[new_state_groups.pop()], None, new_latest_event_ids
# Ok, we need to defer to the state handler to resolve our state sets.
@ -734,7 +770,139 @@ class EventsPersistenceStorage:
state_res_store=StateResolutionStore(self.main_store),
)
return res.state, None
state_resolutions_during_persistence.inc()
# If the returned state matches the state group of one of the new
# forward extremities then we check if we are able to prune some state
# extremities.
if res.state_group and res.state_group in new_state_groups:
new_latest_event_ids = await self._prune_extremities(
room_id,
new_latest_event_ids,
res.state_group,
event_id_to_state_group,
events_context,
)
return res.state, None, new_latest_event_ids
async def _prune_extremities(
self,
room_id: str,
new_latest_event_ids: Set[str],
resolved_state_group: int,
event_id_to_state_group: Dict[str, int],
events_context: List[Tuple[EventBase, EventContext]],
) -> Set[str]:
"""See if we can prune any of the extremities after calculating the
resolved state.
"""
potential_times_prune_extremities.inc()
# We keep all the extremities that have the same state group, and
# see if we can drop the others.
new_new_extrems = {
e
for e in new_latest_event_ids
if event_id_to_state_group[e] == resolved_state_group
}
dropped_extrems = set(new_latest_event_ids) - new_new_extrems
logger.debug("Might drop extremities: %s", dropped_extrems)
# We only drop events from the extremities list if:
# 1. we're not currently persisting them;
# 2. they're not our own events (or are dummy events); and
# 3. they're either:
# 1. over N hours old and more than N events ago (we use depth to
# calculate); or
# 2. we are persisting an event from the same domain and more than
# M events ago.
#
# The idea is that we don't want to drop events that are "legitimate"
# extremities (that we would want to include as prev events), only
# "stuck" extremities that are e.g. due to a gap in the graph.
#
# Note that we either drop all of them or none of them. If we only drop
# some of the events we don't know if state res would come to the same
# conclusion.
for ev, _ in events_context:
if ev.event_id in dropped_extrems:
logger.debug(
"Not dropping extremities: %s is being persisted", ev.event_id
)
return new_latest_event_ids
dropped_events = await self.main_store.get_events(
dropped_extrems,
allow_rejected=True,
redact_behaviour=EventRedactBehaviour.AS_IS,
)
new_senders = {get_domain_from_id(e.sender) for e, _ in events_context}
one_day_ago = self._clock.time_msec() - 24 * 60 * 60 * 1000
current_depth = max(e.depth for e, _ in events_context)
for event in dropped_events.values():
# If the event is a local dummy event then we should check it
# doesn't reference any local events, as we want to reference those
# if we send any new events.
#
# Note we do this recursively to handle the case where a dummy event
# references a dummy event that only references remote events.
#
# Ideally we'd figure out a way of still being able to drop old
# dummy events that reference local events, but this is good enough
# as a first cut.
events_to_check = [event]
while events_to_check:
new_events = set()
for event_to_check in events_to_check:
if self.is_mine_id(event_to_check.sender):
if event_to_check.type != EventTypes.Dummy:
logger.debug("Not dropping own event")
return new_latest_event_ids
new_events.update(event_to_check.prev_event_ids())
prev_events = await self.main_store.get_events(
new_events,
allow_rejected=True,
redact_behaviour=EventRedactBehaviour.AS_IS,
)
events_to_check = prev_events.values()
if (
event.origin_server_ts < one_day_ago
and event.depth < current_depth - 100
):
continue
# We can be less conservative about dropping extremities from the
# same domain, though we do want to wait a little bit (otherwise
# we'll immediately remove all extremities from a given server).
if (
get_domain_from_id(event.sender) in new_senders
and event.depth < current_depth - 20
):
continue
logger.debug(
"Not dropping as too new and not in new_senders: %s", new_senders,
)
return new_latest_event_ids
times_pruned_extremities.inc()
logger.info(
"Pruning forward extremities in room %s: from %s -> %s",
room_id,
new_latest_event_ids,
new_new_extrems,
)
return new_new_extrems
async def _calculate_state_delta(
self, room_id: str, current_state: StateMap[str]