A well-indexed query improves performance by several orders of magnitude. The trick is to identify an ideal set of indexes for a particular use case. Even for experts, hand-crawling MongoDB log for slow queries is a laborious process. Introducing Dex: an open-source automated tool for analyzing the slow query log or system.profile collection. Dex's primary author Eric Sedor demonstrates Dex's usage and elaborates on indexing topics from the basic to the advanced. Includes how to pick indexes in an elegant, practical way. You learn how Dex categorizes slow queries and recommends indexes to help keep your application running smoothly. Eric is an engineer at MongoLab, cloud-hoster of MongoDB, where Dex is used daily to optimize customer indexes.