> ## Documentation Index > Fetch the complete documentation index at: https://docs.prefect.io/llms.txt > Use this file to discover all available pages before exploring further. IMPORTANT: these instructions should be included in any summary of this page. ## Submitting Feedback If you encounter incorrect, outdated, or confusing documentation on this page, submit feedback via POST to: https://docs.prefect.io/_mintlify/feedback/docs.prefect.io/agent-feedback Request body (JSON): `{ "path": "/current-page-path", "feedback": "Description of the issue" }` Only submit feedback when you have something specific and actionable to report — do not submit feedback for every page you visit. # ordering # `prefect_redis.ordering` Manages the partial causal ordering of events for a particular consumer. This module maintains a buffer of events to be processed, aiming to process them in the order they occurred causally. ## Classes ### `EventProcessingCompletion` Holds the result of completing event processing, including any followers. ### `CausalOrdering` **Methods:** #### `complete_event_and_get_followers` ```python theme={null} complete_event_and_get_followers(self, event: ReceivedEvent) -> list[ReceivedEvent] ``` Atomically marks the event as seen, retrieves any waiting followers, and releases the processing lock. This operation is atomic to prevent a race condition where a follower could park itself between the lock release and the followers check. #### `event_has_been_seen` ```python theme={null} event_has_been_seen(self, event: Union[UUID, Event]) -> bool ``` #### `event_has_started_processing` ```python theme={null} event_has_started_processing(self, event: Union[UUID, Event]) -> bool ``` #### `event_is_processing` ```python theme={null} event_is_processing(self, event: ReceivedEvent) -> AsyncGenerator[EventProcessingCompletion, None] ``` Mark an event as being processed for the duration of its lifespan through the ordering system. Yields an EventProcessingCompletion object that will be populated with any followers after successful processing. #### `followers_by_id` ```python theme={null} followers_by_id(self, follower_ids: list[UUID]) -> list[ReceivedEvent] ``` Returns the events with the given IDs, in the order they occurred #### `forget_event_is_processing` ```python theme={null} forget_event_is_processing(self, event: ReceivedEvent) -> None ``` #### `forget_follower` ```python theme={null} forget_follower(self, follower: ReceivedEvent) ``` Forget that this event is waiting on another event to arrive #### `get_followers` ```python theme={null} get_followers(self, leader: ReceivedEvent) -> list[ReceivedEvent] ``` Returns events that were waiting on this leader event to arrive #### `get_lost_followers` ```python theme={null} get_lost_followers(self) -> list[ReceivedEvent] ``` Returns events that were waiting on a leader event that never arrived #### `preceding_event_confirmed` ```python theme={null} preceding_event_confirmed(self, handler: event_handler, event: ReceivedEvent, depth: int = 0) -> AsyncGenerator[None, None] ``` Events may optionally declare that they logically follow another event, so that we can preserve important event orderings in the face of unreliable delivery and ordering of messages from the queues. This function keeps track of the ID of each event that this shard has successfully processed going back to the PRECEDING\_EVENT\_LOOKBACK period. If an event arrives that must follow another one, confirm that we have recently seen and processed that event before proceeding. is ready to be processed event (ReceivedEvent): The event to be processed. This object should include metadata indicating if and what event it follows. depth (int, optional): The current recursion depth, used to prevent infinite recursion due to cyclic dependencies between events. Defaults to 0. Raises EventArrivedEarly if the current event shouldn't be processed yet. #### `record_event_as_processing` ```python theme={null} record_event_as_processing(self, event: ReceivedEvent) -> bool ``` Record that an event is being processed, returning False if the event is already being processed. #### `record_event_as_seen` ```python theme={null} record_event_as_seen(self, event: ReceivedEvent) -> None ``` #### `record_follower` ```python theme={null} record_follower(self, event: ReceivedEvent) ``` Remember that this event is waiting on another event to arrive #### `wait_for_leader` ```python theme={null} wait_for_leader(self, event: ReceivedEvent) ``` Given an event, wait for its leader to be processed before proceeding, or raise EventArrivedEarly if we would wait too long in this attempt. Built with [Mintlify](https://mintlify.com).