What mechanisms ensure reliable delivery and safety of events in message queues?

The following mechanisms are used to ensure reliable delivery and preservation of events in the message queue:

• Acknowledgements: the consumer confirms successful processing of a message, and only then is the message removed from the queue.
• Transactions: send and receive message operations are performed within a transaction, which prevents data loss in case of failures.
• Retries: if processing fails, the message can be resent.
• Message durability: messages are saved to disk to prevent loss upon broker restart.
• Message identifiers and deduplication: to avoid duplication during repeated deliveries.

For example, in RabbitMQ, message acknowledgements (ACK), durable queues, and persistent messages are used for reliability, while in Kafka, replication and record acknowledgements (acks) are used to guarantee delivery.