The MongoDB $sum operator is a powerful tool for calculating sums and aggregating data. It allows developers to compute the collective sum of numeric values within a collection, handling missing fields and ignoring non-numeric values. The operator can be used in various aggregation stages like $group, $project, and $addFields to perform complex calculations and optimizations. Its syntax is straightforward, but understanding its behavior is key to using it for its full potential. With the ability to focus on numbers, handle missing data, and be versatile in its application, the $sum operator is an indispensable tool for anyone working with numeric data in MongoDB. By leveraging its power, developers can unlock valuable insights from their data and perform advanced calculations and aggregations. Additionally, learning how to optimize the performance of the $sum operator is essential, especially when dealing with large datasets. SingleStore Kai, a distributed SQL database that provides a MongoDB-compatible API, can significantly accelerate analytical queries, including those using $sum, offering up to 100x faster performance for common workloads.