MongoDB ACID — Part 3: Isolation — Snapshot Isolation and concurrency

Isolation in MongoDB is built from MVCC and Read Concern. This Part 3 walks through dirty reads, non-repeatable reads, phantoms, and read skew without forcing SQL isolation labels onto MongoDB, and clarifies what multi-document transactions with snapshot read concern actually guarantee. It connects fail-on-conflict behavior, client retries, and lock-acquisition timeouts into one mental model, compares local, majority, and snapshot read concerns with replication caveats, spells out prerequisites for causal consistency, and discusses write skew mitigations with their operational trade-offs. Part 4 will continue with durability and Write Concern.