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Update get_pdu to return the original, pristine EventBase (#13320)
Update `get_pdu` to return the untouched, pristine `EventBase` as it was originally seen over federation (no metadata added). Previously, we returned the same `event` reference that we stored in the cache which downstream code modified in place and added metadata like setting it as an `outlier` and essentially poisoned our cache. Now we always return a copy of the `event` so the original can stay pristine in our cache and re-used for the next cache call.
Split out from https://github.com/matrix-org/synapse/pull/13205
As discussed at:
- https://github.com/matrix-org/synapse/pull/13205#discussion_r918365746
- https://github.com/matrix-org/synapse/pull/13205#discussion_r918366125
Related to https://github.com/matrix-org/synapse/issues/12584. This PR doesn't fix that issue because it hits [`get_event` which exists from the local database before it tries to `get_pdu`](7864f33e28/synapse/federation/federation_client.py (L581-L594)).
This commit is contained in:
Eric Eastwood
GitHub
parent
a1b62af2af
commit
0f971ca68e
5 changed files with 232 additions and 60 deletions
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@ -53,7 +53,7 @@ from synapse.api.room_versions import (
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RoomVersion,
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RoomVersions,
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)
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from synapse.events import EventBase, builder
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from synapse.events import EventBase, builder, make_event_from_dict
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from synapse.federation.federation_base import (
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FederationBase,
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InvalidEventSignatureError,
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@ -299,7 +299,8 @@ class FederationClient(FederationBase):
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moving to the next destination. None indicates no timeout.
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Returns:
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The requested PDU, or None if we were unable to find it.
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A copy of the requested PDU that is safe to modify, or None if we
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were unable to find it.
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Raises:
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SynapseError, NotRetryingDestination, FederationDeniedError
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@ -309,7 +310,7 @@ class FederationClient(FederationBase):
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)
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logger.debug(
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"retrieved event id %s from %s: %r",
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"get_pdu_from_destination_raw: retrieved event id %s from %s: %r",
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event_id,
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destination,
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transaction_data,
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@ -358,54 +359,92 @@ class FederationClient(FederationBase):
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The requested PDU, or None if we were unable to find it.
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"""
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logger.debug(
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"get_pdu: event_id=%s from destinations=%s", event_id, destinations
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)
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# TODO: Rate limit the number of times we try and get the same event.
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ev = self._get_pdu_cache.get(event_id)
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if ev:
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return ev
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# We might need the same event multiple times in quick succession (before
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# it gets persisted to the database), so we cache the results of the lookup.
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# Note that this is separate to the regular get_event cache which caches
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# events once they have been persisted.
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event = self._get_pdu_cache.get(event_id)
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pdu_attempts = self.pdu_destination_tried.setdefault(event_id, {})
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# If we don't see the event in the cache, go try to fetch it from the
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# provided remote federated destinations
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if not event:
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pdu_attempts = self.pdu_destination_tried.setdefault(event_id, {})
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signed_pdu = None
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for destination in destinations:
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now = self._clock.time_msec()
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last_attempt = pdu_attempts.get(destination, 0)
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if last_attempt + PDU_RETRY_TIME_MS > now:
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continue
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for destination in destinations:
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now = self._clock.time_msec()
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last_attempt = pdu_attempts.get(destination, 0)
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if last_attempt + PDU_RETRY_TIME_MS > now:
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logger.debug(
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"get_pdu: skipping destination=%s because we tried it recently last_attempt=%s and we only check every %s (now=%s)",
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destination,
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last_attempt,
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PDU_RETRY_TIME_MS,
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now,
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)
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continue
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try:
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signed_pdu = await self.get_pdu_from_destination_raw(
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destination=destination,
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event_id=event_id,
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room_version=room_version,
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timeout=timeout,
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)
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try:
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event = await self.get_pdu_from_destination_raw(
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destination=destination,
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event_id=event_id,
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room_version=room_version,
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timeout=timeout,
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)
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pdu_attempts[destination] = now
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pdu_attempts[destination] = now
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except SynapseError as e:
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logger.info(
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"Failed to get PDU %s from %s because %s", event_id, destination, e
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)
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continue
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except NotRetryingDestination as e:
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logger.info(str(e))
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continue
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except FederationDeniedError as e:
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logger.info(str(e))
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continue
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except Exception as e:
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pdu_attempts[destination] = now
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if event:
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# Prime the cache
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self._get_pdu_cache[event.event_id] = event
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logger.info(
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"Failed to get PDU %s from %s because %s", event_id, destination, e
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)
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continue
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# FIXME: We should add a `break` here to avoid calling every
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# destination after we already found a PDU (will follow-up
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# in a separate PR)
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if signed_pdu:
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self._get_pdu_cache[event_id] = signed_pdu
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except SynapseError as e:
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logger.info(
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"Failed to get PDU %s from %s because %s",
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event_id,
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destination,
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e,
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)
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continue
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except NotRetryingDestination as e:
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logger.info(str(e))
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continue
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except FederationDeniedError as e:
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logger.info(str(e))
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continue
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except Exception as e:
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pdu_attempts[destination] = now
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return signed_pdu
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logger.info(
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"Failed to get PDU %s from %s because %s",
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event_id,
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destination,
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e,
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)
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continue
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if not event:
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return None
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# `event` now refers to an object stored in `get_pdu_cache`. Our
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# callers may need to modify the returned object (eg to set
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# `event.internal_metadata.outlier = true`), so we return a copy
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# rather than the original object.
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event_copy = make_event_from_dict(
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event.get_pdu_json(),
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event.room_version,
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)
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return event_copy
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async def get_room_state_ids(
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self, destination: str, room_id: str, event_id: str
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@ -766,10 +766,24 @@ class FederationEventHandler:
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"""
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logger.info("Processing pulled event %s", event)
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# these should not be outliers.
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assert (
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not event.internal_metadata.is_outlier()
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), "pulled event unexpectedly flagged as outlier"
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# This function should not be used to persist outliers (use something
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# else) because this does a bunch of operations that aren't necessary
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# (extra work; in particular, it makes sure we have all the prev_events
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# and resolves the state across those prev events). If you happen to run
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# into a situation where the event you're trying to process/backfill is
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# marked as an `outlier`, then you should update that spot to return an
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# `EventBase` copy that doesn't have `outlier` flag set.
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#
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# `EventBase` is used to represent both an event we have not yet
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# persisted, and one that we have persisted and now keep in the cache.
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# In an ideal world this method would only be called with the first type
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# of event, but it turns out that's not actually the case and for
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# example, you could get an event from cache that is marked as an
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# `outlier` (fix up that spot though).
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assert not event.internal_metadata.is_outlier(), (
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"Outlier event passed to _process_pulled_event. "
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"To persist an event as a non-outlier, make sure to pass in a copy without `event.internal_metadata.outlier = true`."
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)
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event_id = event.event_id
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@ -1346,9 +1346,24 @@ class PersistEventsStore:
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event_id: outlier for event_id, outlier in txn
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}
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logger.debug(
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"_update_outliers_txn: events=%s have_persisted=%s",
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[ev.event_id for ev, _ in events_and_contexts],
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have_persisted,
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)
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to_remove = set()
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for event, context in events_and_contexts:
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if event.event_id not in have_persisted:
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outlier_persisted = have_persisted.get(event.event_id)
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logger.debug(
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"_update_outliers_txn: event=%s outlier=%s outlier_persisted=%s",
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event.event_id,
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event.internal_metadata.is_outlier(),
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outlier_persisted,
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)
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# Ignore events which we haven't persisted at all
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if outlier_persisted is None:
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continue
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to_remove.add(event)
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@ -1358,7 +1373,6 @@ class PersistEventsStore:
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# was an outlier or not - what we have is at least as good.
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continue
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outlier_persisted = have_persisted[event.event_id]
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if not event.internal_metadata.is_outlier() and outlier_persisted:
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# We received a copy of an event that we had already stored as
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# an outlier in the database. We now have some state at that event
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@ -1369,7 +1383,10 @@ class PersistEventsStore:
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# events down /sync. In general they will be historical events, so that
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# doesn't matter too much, but that is not always the case.
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logger.info("Updating state for ex-outlier event %s", event.event_id)
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logger.info(
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"_update_outliers_txn: Updating state for ex-outlier event %s",
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event.event_id,
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)
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# insert into event_to_state_groups.
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try:
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