Does MongoDB ensure compliance with ACID transactional principles?

MongoDB was not originally designed to fully comply with ACID transactions, as it is a document-oriented NoSQL database optimized for scalability and high performance.

However, starting from version 4.0, MongoDB supports multi-document transactions that provide atomicity, consistency, isolation, and durability (ACID) within a replica set. In version 4.2, this capability was extended to distributed transactions across multiple shards.

Nevertheless, transactions in MongoDB can have overhead and are not always recommended for all scenarios. Often, application architecture in MongoDB is built to minimize the need for complex transactions, using atomic operations at the document level.

Thus, MongoDB provides ACID transactions but with some limitations and specific features that should be considered when designing the system.