7.3. Query optimization

Query optimization is the process of identifying slow queries, discovering why they’re slow, and then taking steps to speed them up. In this section, we’ll look at each step of the query optimization process in turn so that by the time you finish reading, you’ll have a framework for addressing problematic queries on any MongoDB installation.

Before diving in, I must warn that the techniques presented here can’t be used to solve every query performance problem. The causes of slow queries vary too much. Poor application design, inappropriate data models, and insufficient physical hardware are all common culprits, and their remedies require a significant time investment. Here we’ll look at ways to optimize queries by restructuring the queries themselves and by building the most useful indexes. I’ll also describe other avenues for investigation when these techniques fail to deliver.