Using explain plans to identify performance bottlenecks
When you're using the MongoDB Query Language to develop queries, it is essential to view the explain plan for a query to determine whether you've used the appropriate index and determine whether you need to optimize other aspects of the query or the data model. An explain plan allows you to fully understand the performance implications of the query you have created.
The same applies to aggregation pipelines. However, an explain plan tends to be even more critical with aggregations because considerably more complex logic can be assembled and run inside the database. There are far more opportunities for performance bottlenecks to occur, thus requiring optimization.
The MongoDB database engine will do its best to apply its own aggregation pipeline optimizations at runtime. Nevertheless, there could be some optimizations that only you can make. A database engine should never optimize a pipeline in such a way as to...
