> ## 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 ## Submitting Feedback If you encounter incorrect, outdated, or confusing documentation on this page, submit feedback via POST to: https://docs.prefect.io/_mintlify/feedback/docs.prefect.io/agent-feedback Request body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. # memory # `prefect.server.utilities.messaging.memory` ## Functions ### `log_metrics_periodically` ```python theme={null} log_metrics_periodically(interval: float = 2.0) -> None ``` ### `update_metric` ```python theme={null} update_metric(topic: str, key: str, amount: int = 1) -> None ``` ### `break_topic` ```python theme={null} break_topic() ``` ### `ephemeral_subscription` ```python theme={null} ephemeral_subscription(topic: str) -> AsyncGenerator[Mapping[str, Any], None] ``` ## Classes ### `MemoryMessage` ### `Subscription` A subscription to a topic. Messages are delivered to the subscription's queue and retried up to a maximum number of times. If a message cannot be delivered after the maximum number of retries it is moved to the dead letter queue. The dead letter queue is a directory of JSON files containing the serialized message. Messages remain in the dead letter queue until they are removed manually. **Attributes:** * `topic`: The topic that the subscription receives messages from. * `max_retries`: The maximum number of times a message will be retried for this subscription. * `dead_letter_queue_path`: The path to the dead letter queue folder. **Methods:** #### `deliver` ```python theme={null} deliver(self, message: MemoryMessage) -> None ``` Deliver a message to the subscription's queue. **Args:** * `message`: The message to deliver. #### `get` ```python theme={null} get(self) -> MemoryMessage ``` Get a message from the subscription's queue. #### `retry` ```python theme={null} retry(self, message: MemoryMessage) -> None ``` Place a message back on the retry queue. If the message has retried more than the maximum number of times it is moved to the dead letter queue. **Args:** * `message`: The message to retry. #### `send_to_dead_letter_queue` ```python theme={null} send_to_dead_letter_queue(self, message: MemoryMessage) -> None ``` Send a message to the dead letter queue. The dead letter queue is a directory of JSON files containing the serialized messages. **Args:** * `message`: The message to send to the dead letter queue. ### `Topic` **Methods:** #### `by_name` ```python theme={null} by_name(cls, name: str) -> 'Topic' ``` #### `clear` ```python theme={null} clear(self) -> None ``` #### `clear_all` ```python theme={null} clear_all(cls) -> None ``` #### `publish` ```python theme={null} publish(self, message: MemoryMessage) -> None ``` #### `subscribe` ```python theme={null} subscribe(self, **subscription_kwargs: Any) -> Subscription ``` #### `unsubscribe` ```python theme={null} unsubscribe(self, subscription: Subscription) -> None ``` ### `Cache` **Methods:** #### `clear_recently_seen_messages` ```python theme={null} clear_recently_seen_messages(self) -> None ``` #### `forget_duplicates` ```python theme={null} forget_duplicates(self, attribute: str, messages: Iterable[M]) -> None ``` #### `without_duplicates` ```python theme={null} without_duplicates(self, attribute: str, messages: Iterable[M]) -> list[M] ``` ### `Publisher` **Methods:** #### `publish_data` ```python theme={null} publish_data(self, data: bytes, attributes: Mapping[str, str]) -> None ``` ### `Consumer` **Methods:** #### `cleanup` ```python theme={null} cleanup(self) -> None ``` Cleanup resources by unsubscribing from the topic. This should be called when the consumer is no longer needed to prevent memory leaks from orphaned subscriptions. #### `run` ```python theme={null} run(self, handler: MessageHandler) -> None ``` Built with [Mintlify](https://mintlify.com).