In the previous blog in this series, we learned how to produce, read and interpret execution plans. We learned that an execution plan provides information about access methods, which PostgreSQL use to select records from a database. Specifically, we observed that in some cases PostgreSQL used sequential scan, and in some cases index-based access.
It might seem to be a better idea to talk about indexes before we discussed execution plans, but query plans are a good place to start the performance journey and work our way in! This blog is going to be about indexes, why we need them,