---
title: memory
sidebarTitle: memory
---

# `prefect.server.events.ordering.memory`

## Classes

### `EventBeingProcessed` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L32" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Indicates that an event is currently being processed and should not be processed
until it is finished. This may happen due to concurrent processing.


### `CausalOrdering` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L40" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

**Methods:**

#### `clear` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L71" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
clear(self) -> None
```

Clear all data for this scope.


#### `clear_all_scopes` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L80" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
clear_all_scopes(cls) -> None
```

Clear all data for all scopes - useful for testing.


#### `event_has_been_seen` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L104" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
event_has_been_seen(self, event: UUID | Event) -> bool
```

#### `event_has_started_processing` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L95" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
event_has_started_processing(self, event: UUID | Event) -> bool
```

#### `event_is_processing` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L188" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
event_is_processing(self, event: ReceivedEvent) -> AsyncGenerator[None, None]
```

Mark an event as being processed for the duration of its lifespan through
the ordering system.


#### `followers_by_id` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L149" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
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` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L100" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
forget_event_is_processing(self, event: ReceivedEvent) -> None
```

#### `forget_follower` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L124" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
forget_follower(self, follower: ReceivedEvent) -> None
```

Forget that this event is waiting on another event to arrive.


#### `get_followers` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L136" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
get_followers(self, leader: ReceivedEvent) -> list[ReceivedEvent]
```

Returns events that were waiting on this leader event to arrive.


#### `get_lost_followers` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L158" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
get_lost_followers(self) -> list[ReceivedEvent]
```

Returns events that were waiting on a leader event that never arrived.


#### `preceding_event_confirmed` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L243" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
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.

**Args:**
- `handler`: The function to call when an out-of-order event is
ready to be processed
- `event`: The event to be processed. This object should include
metadata indicating if and what event it follows.
- `depth`: 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` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L87" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
record_event_as_processing(self, event: ReceivedEvent) -> bool
```

Record that an event is being processed, returning False if already processing.


#### `record_event_as_seen` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L109" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
record_event_as_seen(self, event: ReceivedEvent) -> None
```

#### `record_follower` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L113" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
record_follower(self, event: ReceivedEvent) -> None
```

Remember that this event is waiting on another event to arrive.


#### `wait_for_leader` <sup><a href="https://github.com/PrefectHQ/prefect/blob/main/src/prefect/server/events/ordering/memory.py#L203" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
wait_for_leader(self, event: ReceivedEvent) -> None
```

Given an event, wait for its leader to be processed before proceeding, or
raise EventArrivedEarly if we would wait too long in this attempt.

