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Whenever we want to persist an event, we first compute an event context, which includes the state at the event and a flag indicating whether the state is partial. After a lot of processing, we finally try to store the event in the database, which can fail for partial state events when the containing room has been un-partial stated in the meantime. We detect the race as a foreign key constraint failure in the data store layer and turn it into a special `PartialStateConflictError` exception, which makes its way up to the method in which we computed the event context. To make things difficult, the exception needs to cross a replication request: `/fed_send_events` for events coming over federation and `/send_event` for events from clients. We transport the `PartialStateConflictError` as a `409 Conflict` over replication and turn `409`s back into `PartialStateConflictError`s on the worker making the request. All client events go through `EventCreationHandler.handle_new_client_event`, which is called in *a lot* of places. Instead of trying to update all the code which creates client events, we turn the `PartialStateConflictError` into a `429 Too Many Requests` in `EventCreationHandler.handle_new_client_event` and hope that clients take it as a hint to retry their request. On the federation event side, there are 7 places which compute event contexts. 4 of them use outlier event contexts: `FederationEventHandler._auth_and_persist_outliers_inner`, `FederationHandler.do_knock`, `FederationHandler.on_invite_request` and `FederationHandler.do_remotely_reject_invite`. These events won't have the partial state flag, so we do not need to do anything for then. The remaining 3 paths which create events are `FederationEventHandler.process_remote_join`, `FederationEventHandler.on_send_membership_event` and `FederationEventHandler._process_received_pdu`. We can't experience the race in `process_remote_join`, unless we're handling an additional join into a partial state room, which currently blocks, so we make no attempt to handle it correctly. `on_send_membership_event` is only called by `FederationServer._on_send_membership_event`, so we catch the `PartialStateConflictError` there and retry just once. `_process_received_pdu` is called by `on_receive_pdu` for incoming events and `_process_pulled_event` for backfill. The latter should never try to persist partial state events, so we ignore it. We catch the `PartialStateConflictError` in `on_receive_pdu` and retry just once. Refering to the graph of code paths in https://github.com/matrix-org/synapse/issues/12988#issuecomment-1156857648 may make the above make more sense. Signed-off-by: Sean Quah <seanq@matrix.org> |
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| .. | ||
| ui_auth | ||
| __init__.py | ||
| account_data.py | ||
| account_validity.py | ||
| account.py | ||
| admin.py | ||
| appservice.py | ||
| auth.py | ||
| cas.py | ||
| deactivate_account.py | ||
| device.py | ||
| devicemessage.py | ||
| directory.py | ||
| e2e_keys.py | ||
| e2e_room_keys.py | ||
| event_auth.py | ||
| events.py | ||
| federation_event.py | ||
| federation.py | ||
| identity.py | ||
| initial_sync.py | ||
| message.py | ||
| oidc.py | ||
| pagination.py | ||
| password_policy.py | ||
| presence.py | ||
| profile.py | ||
| push_rules.py | ||
| read_marker.py | ||
| receipts.py | ||
| register.py | ||
| relations.py | ||
| room_batch.py | ||
| room_list.py | ||
| room_member_worker.py | ||
| room_member.py | ||
| room_summary.py | ||
| room.py | ||
| saml.py | ||
| search.py | ||
| send_email.py | ||
| set_password.py | ||
| sso.py | ||
| state_deltas.py | ||
| stats.py | ||
| sync.py | ||
| typing.py | ||
| user_directory.py | ||