MongoDB implementation of ACID

MongoDB ensures atomicity for single-document operations, and this is enough for most real-world cases. However, sectors such as finance and fintech, with stringent requirements, demand different treatment in MongoDB. In the case of financial and banking sectors, applications often handle huge numbers of accounts and financial transactions, all of which need verification. These transactions often span multiple documents—thousands or more.

Generally, multi-document ACID transactions are used when an unbounded number of entities that cannot fit into an array of subdocuments as the main document, outgrow the maximum BSON document size (16MB, currently supported by MongoDB). If you're experienced in relational database management systems (RDBMS), you will find MongoDB's multi-document semantics very familiar and straightforward.

According to a MongoDB seminal white paper on ACID transactions (https://www.mongodb.com/collateral/mongodb...