java MongoDB 4.0 introduces support for multi-document ACID transactions, extending the transactional guarantees across multiple documents, collections, and databases. This feature allows developers to ensure atomicity and consistency in their applications, particularly when dealing with complex business logic or distributed systems. By using multi-document transactions, developers can avoid issues such as partial updates or inconsistent data, which can arise from independent operations on separate documents or collections. The new feature builds upon MongoDB's existing single-document transactional capabilities and provides a more robust and reliable way to manage concurrent updates in large datasets.```java