What exactly did you do with the messages (processing)? How resource-intensive was the processing?

During message processing (processing), I usually performed the following steps:

1. Receiving a message from a queue or broker (e.g., Kafka, RabbitMQ).
2. Validation and parsing of data.
3. Executing business logic — for example, transforming data, calling external services, writing to a database.
4. Error handling and retries if necessary.

The heaviness of processing depended on the task. In some cases, it was a simple operation, such as updating a status in the database, which took milliseconds. In others — complex calculations or integration with external systems, which could take seconds and required asynchronous approach or batching.

To optimize heavy operations, I used:

• Parallel processing using thread pools.
• Caching intermediate data.
• Asynchronous calls and deferred processing.

Example: processing messages with a REST API call and recording the result in a database, where the delay on the external service was the main load.