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Refactor `EventContext` (#12689) 

Refactor how the `EventContext` class works, with the intention of reducing the amount of state we fetch from the DB during event processing.

The idea here is to get rid of the cached `current_state_ids` and `prev_state_ids` that live in the `EventContext`, and instead defer straight to the database (and its caching). 

One change that may have a noticeable effect is that we now no longer prefill the `get_current_state_ids` cache on a state change. However, that query is relatively light, since its just a case of reading a table from the DB (unlike fetching state at an event which is more heavyweight). For deployments with workers this cache isn't even used.


Part of #12684
This commit is contained in:
Erik Johnston 2022-05-10 20:43:13 +01:00 committed by GitHub
parent c997bfb926
commit c72d26c1e1
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13 changed files with 70 additions and 200 deletions
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1
changelog.d/12689.misc Normal file
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@ -0,0 +1 @@
Refactor `EventContext` class.

177
synapse/events/snapshot.py
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@ -17,11 +17,8 @@ import attr
from frozendict import frozendict
from typing_extensions import Literal
from twisted.internet.defer import Deferred
from synapse.appservice import ApplicationService
from synapse.events import EventBase
from synapse.logging.context import make_deferred_yieldable, run_in_background
from synapse.types import JsonDict, StateMap
if TYPE_CHECKING:
@ -61,6 +58,9 @@ class EventContext:
If ``state_group`` is None (ie, the event is an outlier),
``state_group_before_event`` will always also be ``None``.
state_delta_due_to_event: If `state_group` and `state_group_before_event` are not None
then this is the delta of the state between the two groups.
prev_group: If it is known, ``state_group``'s prev_group. Note that this being
None does not necessarily mean that ``state_group`` does not have
a prev_group!
@ -79,73 +79,47 @@ class EventContext:
app_service: If this event is being sent by a (local) application service, that
app service.
_current_state_ids: The room state map, including this event - ie, the state
in ``state_group``.
(type, state_key) -> event_id
For an outlier, this is {}
Note that this is a private attribute: it should be accessed via
``get_current_state_ids``. _AsyncEventContext impl calculates this
on-demand: it will be None until that happens.
_prev_state_ids: The room state map, excluding this event - ie, the state
in ``state_group_before_event``. For a non-state
event, this will be the same as _current_state_events.
Note that it is a completely different thing to prev_group!
(type, state_key) -> event_id
For an outlier, this is {}
As with _current_state_ids, this is a private attribute. It should be
accessed via get_prev_state_ids.
partial_state: if True, we may be storing this event with a temporary,
incomplete state.
"""
_storage: "Storage"
rejected: Union[Literal[False], str] = False
_state_group: Optional[int] = None
state_group_before_event: Optional[int] = None
_state_delta_due_to_event: Optional[StateMap[str]] = None
prev_group: Optional[int] = None
delta_ids: Optional[StateMap[str]] = None
app_service: Optional[ApplicationService] = None
_current_state_ids: Optional[StateMap[str]] = None
_prev_state_ids: Optional[StateMap[str]] = None
partial_state: bool = False
@staticmethod
def with_state(
storage: "Storage",
state_group: Optional[int],
state_group_before_event: Optional[int],
current_state_ids: Optional[StateMap[str]],
prev_state_ids: Optional[StateMap[str]],
state_delta_due_to_event: Optional[StateMap[str]],
partial_state: bool,
prev_group: Optional[int] = None,
delta_ids: Optional[StateMap[str]] = None,
) -> "EventContext":
return EventContext(
current_state_ids=current_state_ids,
prev_state_ids=prev_state_ids,
storage=storage,
state_group=state_group,
state_group_before_event=state_group_before_event,
state_delta_due_to_event=state_delta_due_to_event,
prev_group=prev_group,
delta_ids=delta_ids,
partial_state=partial_state,
)
@staticmethod
def for_outlier() -> "EventContext":
def for_outlier(
storage: "Storage",
) -> "EventContext":
"""Return an EventContext instance suitable for persisting an outlier event"""
return EventContext(
current_state_ids={},
prev_state_ids={},
)
return EventContext(storage=storage)
async def serialize(self, event: EventBase, store: "DataStore") -> JsonDict:
"""Converts self to a type that can be serialized as JSON, and then
@ -158,24 +132,14 @@ class EventContext:
The serialized event.
"""
# We don't serialize the full state dicts, instead they get pulled out
# of the DB on the other side. However, the other side can't figure out
# the prev_state_ids, so if we're a state event we include the event
# id that we replaced in the state.
if event.is_state():
prev_state_ids = await self.get_prev_state_ids()
prev_state_id = prev_state_ids.get((event.type, event.state_key))
else:
prev_state_id = None
return {
"prev_state_id": prev_state_id,
"event_type": event.type,
"event_state_key": event.get_state_key(),
"state_group": self._state_group,
"state_group_before_event": self.state_group_before_event,
"rejected": self.rejected,
"prev_group": self.prev_group,
"state_delta_due_to_event": _encode_state_dict(
self._state_delta_due_to_event
),
"delta_ids": _encode_state_dict(self.delta_ids),
"app_service_id": self.app_service.id if self.app_service else None,
"partial_state": self.partial_state,
@ -193,16 +157,16 @@ class EventContext:
Returns:
The event context.
"""
context = _AsyncEventContextImpl(
context = EventContext(
# We use the state_group and prev_state_id stuff to pull the
# current_state_ids out of the DB and construct prev_state_ids.
storage=storage,
prev_state_id=input["prev_state_id"],
event_type=input["event_type"],
event_state_key=input["event_state_key"],
state_group=input["state_group"],
state_group_before_event=input["state_group_before_event"],
prev_group=input["prev_group"],
state_delta_due_to_event=_decode_state_dict(
input["state_delta_due_to_event"]
),
delta_ids=_decode_state_dict(input["delta_ids"]),
rejected=input["rejected"],
partial_state=input.get("partial_state", False),
@ -250,8 +214,15 @@ class EventContext:
if self.rejected:
raise RuntimeError("Attempt to access state_ids of rejected event")
await self._ensure_fetched()
return self._current_state_ids
assert self._state_delta_due_to_event is not None
prev_state_ids = await self.get_prev_state_ids()
if self._state_delta_due_to_event:
prev_state_ids = dict(prev_state_ids)
prev_state_ids.update(self._state_delta_due_to_event)
return prev_state_ids
async def get_prev_state_ids(self) -> StateMap[str]:
"""
@ -266,94 +237,10 @@ class EventContext:
Maps a (type, state_key) to the event ID of the state event matching
this tuple.
"""
await self._ensure_fetched()
# There *should* be previous state IDs now.
assert self._prev_state_ids is not None
return self._prev_state_ids
def get_cached_current_state_ids(self) -> Optional[StateMap[str]]:
"""Gets the current state IDs if we have them already cached.
It is an error to access this for a rejected event, since rejected state should
not make it into the room state. This method will raise an exception if
``rejected`` is set.
Returns:
Returns None if we haven't cached the state or if state_group is None
(which happens when the associated event is an outlier).
Otherwise, returns the the current state IDs.
"""
if self.rejected:
raise RuntimeError("Attempt to access state_ids of rejected event")
return self._current_state_ids
async def _ensure_fetched(self) -> None:
return None
@attr.s(slots=True)
class _AsyncEventContextImpl(EventContext):
"""
An implementation of EventContext which fetches _current_state_ids and
_prev_state_ids from the database on demand.
Attributes:
_storage
_fetching_state_deferred: Resolves when *_state_ids have been calculated.
None if we haven't started calculating yet
_event_type: The type of the event the context is associated with.
_event_state_key: The state_key of the event the context is associated with.
_prev_state_id: If the event associated with the context is a state event,
then `_prev_state_id` is the event_id of the state that was replaced.
"""
# This needs to have a default as we're inheriting
_storage: "Storage" = attr.ib(default=None)
_prev_state_id: Optional[str] = attr.ib(default=None)
_event_type: str = attr.ib(default=None)
_event_state_key: Optional[str] = attr.ib(default=None)
_fetching_state_deferred: Optional["Deferred[None]"] = attr.ib(default=None)
async def _ensure_fetched(self) -> None:
if not self._fetching_state_deferred:
self._fetching_state_deferred = run_in_background(self._fill_out_state)
await make_deferred_yieldable(self._fetching_state_deferred)
async def _fill_out_state(self) -> None:
"""Called to populate the _current_state_ids and _prev_state_ids
attributes by loading from the database.
"""
if self.state_group is None:
# No state group means the event is an outlier. Usually the state_ids dicts are also
# pre-set to empty dicts, but they get reset when the context is serialized, so set
# them to empty dicts again here.
self._current_state_ids = {}
self._prev_state_ids = {}
return
current_state_ids = await self._storage.state.get_state_ids_for_group(
self.state_group
assert self.state_group_before_event is not None
return await self._storage.state.get_state_ids_for_group(
self.state_group_before_event
)
# Set this separately so mypy knows current_state_ids is not None.
self._current_state_ids = current_state_ids
if self._event_state_key is not None:
self._prev_state_ids = dict(current_state_ids)
key = (self._event_type, self._event_state_key)
if self._prev_state_id:
self._prev_state_ids[key] = self._prev_state_id
else:
self._prev_state_ids.pop(key, None)
else:
self._prev_state_ids = current_state_ids
def _encode_state_dict(

6
synapse/handlers/federation.py
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@ -659,7 +659,7 @@ class FederationHandler:
# in the invitee's sync stream. It is stripped out for all other local users.
event.unsigned["knock_room_state"] = stripped_room_state["knock_state_events"]
context = EventContext.for_outlier()
context = EventContext.for_outlier(self.storage)
stream_id = await self._federation_event_handler.persist_events_and_notify(
event.room_id, [(event, context)]
)
@ -848,7 +848,7 @@ class FederationHandler:
)
)
context = EventContext.for_outlier()
context = EventContext.for_outlier(self.storage)
await self._federation_event_handler.persist_events_and_notify(
event.room_id, [(event, context)]
)
@ -877,7 +877,7 @@ class FederationHandler:
await self.federation_client.send_leave(host_list, event)
context = EventContext.for_outlier()
context = EventContext.for_outlier(self.storage)
stream_id = await self._federation_event_handler.persist_events_and_notify(
event.room_id, [(event, context)]
)

6
synapse/handlers/federation_event.py
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@ -1423,7 +1423,7 @@ class FederationEventHandler:
# we're not bothering about room state, so flag the event as an outlier.
event.internal_metadata.outlier = True
context = EventContext.for_outlier()
context = EventContext.for_outlier(self._storage)
try:
validate_event_for_room_version(room_version_obj, event)
check_auth_rules_for_event(room_version_obj, event, auth)
@ -1874,10 +1874,10 @@ class FederationEventHandler:
)
return EventContext.with_state(
storage=self._storage,
state_group=state_group,
state_group_before_event=context.state_group_before_event,
current_state_ids=current_state_ids,
prev_state_ids=prev_state_ids,
state_delta_due_to_event=state_updates,
prev_group=prev_group,
delta_ids=state_updates,
partial_state=context.partial_state,

6
synapse/handlers/message.py
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@ -757,6 +757,10 @@ class EventCreationHandler:
The previous version of the event is returned, if it is found in the
event context. Otherwise, None is returned.
"""
if event.internal_metadata.is_outlier():
# This can happen due to out of band memberships
return None
prev_state_ids = await context.get_prev_state_ids()
prev_event_id = prev_state_ids.get((event.type, event.state_key))
if not prev_event_id:
@ -1001,7 +1005,7 @@ class EventCreationHandler:
# after it is created
if builder.internal_metadata.outlier:
event.internal_metadata.outlier = True
context = EventContext.for_outlier()
context = EventContext.for_outlier(self.storage)
elif (
event.type == EventTypes.MSC2716_INSERTION
and state_event_ids

4
synapse/push/action_generator.py
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@ -40,5 +40,9 @@ class ActionGenerator:
async def handle_push_actions_for_event(
self, event: EventBase, context: EventContext
) -> None:
if event.internal_metadata.is_outlier():
# This can happen due to out of band memberships
return
with Measure(self.clock, "action_for_event_by_user"):
await self.bulk_evaluator.action_for_event_by_user(event, context)

9
synapse/state/__init__.py
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@ -130,6 +130,7 @@ class StateHandler:
self.state_store = hs.get_storage().state
self.hs = hs
self._state_resolution_handler = hs.get_state_resolution_handler()
self._storage = hs.get_storage()
@overload
async def get_current_state(
@ -361,10 +362,10 @@ class StateHandler:
if not event.is_state():
return EventContext.with_state(
storage=self._storage,
state_group_before_event=state_group_before_event,
state_group=state_group_before_event,
current_state_ids=state_ids_before_event,
prev_state_ids=state_ids_before_event,
state_delta_due_to_event={},
prev_group=state_group_before_event_prev_group,
delta_ids=deltas_to_state_group_before_event,
partial_state=partial_state,
@ -393,10 +394,10 @@ class StateHandler:
)
return EventContext.with_state(
storage=self._storage,
state_group=state_group_after_event,
state_group_before_event=state_group_before_event,
current_state_ids=state_ids_after_event,
prev_state_ids=state_ids_before_event,
state_delta_due_to_event=delta_ids,
prev_group=state_group_before_event,
delta_ids=delta_ids,
partial_state=partial_state,

6
synapse/storage/databases/main/events.py
View File

@ -128,7 +128,6 @@ class PersistEventsStore:
self,
events_and_contexts: List[Tuple[EventBase, EventContext]],
*,
current_state_for_room: Dict[str, StateMap[str]],
state_delta_for_room: Dict[str, DeltaState],
new_forward_extremities: Dict[str, Set[str]],
use_negative_stream_ordering: bool = False,
@ -139,8 +138,6 @@ class PersistEventsStore:
Args:
events_and_contexts:
current_state_for_room: Map from room_id to the current state of
the room based on forward extremities
state_delta_for_room: Map from room_id to the delta to apply to
room state
new_forward_extremities: Map from room_id to set of event IDs
@ -215,9 +212,6 @@ class PersistEventsStore:
event_counter.labels(event.type, origin_type, origin_entity).inc()
for room_id, new_state in current_state_for_room.items():
self.store.get_current_state_ids.prefill((room_id,), new_state)
for room_id, latest_event_ids in new_forward_extremities.items():
self.store.get_latest_event_ids_in_room.prefill(
(room_id,), list(latest_event_ids)

42
synapse/storage/persist_events.py
View File

@ -487,12 +487,6 @@ class EventsPersistenceStorage:
# extremities in each room
new_forward_extremities: Dict[str, Set[str]] = {}
# map room_id->(type,state_key)->event_id tracking the full
# state in each room after adding these events.
# This is simply used to prefill the get_current_state_ids
# cache
current_state_for_room: Dict[str, StateMap[str]] = {}
# map room_id->(to_delete, to_insert) where to_delete is a list
# of type/state keys to remove from current state, and to_insert
# is a map (type,key)->event_id giving the state delta in each
@ -628,14 +622,8 @@ class EventsPersistenceStorage:
state_delta_for_room[room_id] = delta
# If we have the current_state then lets prefill
# the cache with it.
if current_state is not None:
current_state_for_room[room_id] = current_state
await self.persist_events_store._persist_events_and_state_updates(
chunk,
current_state_for_room=current_state_for_room,
state_delta_for_room=state_delta_for_room,
new_forward_extremities=new_forward_extremities,
use_negative_stream_ordering=backfilled,
@ -733,7 +721,8 @@ class EventsPersistenceStorage:
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.
there has been no change. Either or neither can be None if there
has been a change.
The function may prune some old entries from the set of new
forward extremities if it's safe to do so.
@ -743,9 +732,6 @@ class EventsPersistenceStorage:
the new current state is only returned if we've already calculated
it.
"""
# map from state_group to ((type, key) -> event_id) state map
state_groups_map = {}
# Map from (prev state group, new state group) -> delta state dict
state_group_deltas = {}
@ -759,16 +745,6 @@ class EventsPersistenceStorage:
)
continue
if ctx.state_group in state_groups_map:
continue
# We're only interested in pulling out state that has already
# been cached in the context. We'll pull stuff out of the DB later
# if necessary.
current_state_ids = ctx.get_cached_current_state_ids()
if current_state_ids is not None:
state_groups_map[ctx.state_group] = current_state_ids
if ctx.prev_group:
state_group_deltas[(ctx.prev_group, ctx.state_group)] = ctx.delta_ids
@ -826,18 +802,14 @@ class EventsPersistenceStorage:
delta_ids = state_group_deltas.get((old_state_group, new_state_group), None)
if delta_ids is not None:
# We have a delta from the existing to new current state,
# so lets just return that. If we happen to already have
# 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, new_latest_event_ids
# so lets just return that.
return None, 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.
missing_state = new_state_groups - set(state_groups_map)
if missing_state:
group_to_state = await self.state_store._get_state_for_groups(missing_state)
state_groups_map.update(group_to_state)
state_groups_map = await self.state_store._get_state_for_groups(
new_state_groups
)
if len(new_state_groups) == 1:
# If there is only one state group, then we know what the current

4
tests/handlers/test_federation_event.py
View File

@ -148,7 +148,9 @@ class FederationEventHandlerTests(unittest.FederatingHomeserverTestCase):
prev_event.internal_metadata.outlier = True
persistence = self.hs.get_storage().persistence
self.get_success(
persistence.persist_event(prev_event, EventContext.for_outlier())
persistence.persist_event(
prev_event, EventContext.for_outlier(self.hs.get_storage())
)
)
else:

2
tests/storage/test_event_chain.py
View File

@ -393,7 +393,7 @@ class EventChainStoreTestCase(HomeserverTestCase):
# We need to persist the events to the events and state_events
# tables.
persist_events_store._store_event_txn(
txn, [(e, EventContext()) for e in events]
txn, [(e, EventContext(self.hs.get_storage())) for e in events]
)
# Actually call the function that calculates the auth chain stuff.

3
tests/test_state.py
View File

@ -88,6 +88,9 @@ class _DummyStore:
return groups
async def get_state_ids_for_group(self, state_group):
return self._group_to_state[state_group]
async def store_state_group(
self, event_id, room_id, prev_group, delta_ids, current_state_ids
):

4
tests/test_visibility.py
View File

@ -234,7 +234,9 @@ class FilterEventsForServerTestCase(unittest.HomeserverTestCase):
event = self.get_success(builder.build(prev_event_ids=[], auth_event_ids=[]))
event.internal_metadata.outlier = True
self.get_success(
self.storage.persistence.persist_event(event, EventContext.for_outlier())
self.storage.persistence.persist_event(
event, EventContext.for_outlier(self.storage)
)
)
return event