MongoDB 4.2 has introduced several performance boosts, including improved handling of large documents, accelerated aggregation operations, optimized array processing, and enhanced index builds. The new Optimized Index Builds feature reduces the resource cost of indexing and lowers the cost of inserting new entries into indexes, resulting in improved performance testing and quicker indexing. However, a notable slowdown is observed when bulk inserting new documents with unique values for certain fields on collections with multiple unique indexes, where the search for duplicates can be slowed down by up to 22%. Despite this, the MongoDB team has extensively tested the release and fixed all but one regression before its final release.