MongoDB 4.2 introduces new compression options, including Zstd, which offers higher compression rates while using less CPU compared to other algorithms. The default compression option remains snappy. Additionally, the feature of rotatable keys allows database nodes to use multiple configuration files with different keys, making it easier to update and manage cluster configurations without downtime. Configuration expansion also enables config files to retrieve values from REST endpoints or executable processes, providing a more secure way to manage secrets and configurations.