A new technical guide explains PostgreSQL indexes for developers who understand the concept but want deeper internals. It covers how indexes map keys to row locations (ctid) in the heap, which is divided into 8KB pages. The article demonstrates performance gains using `EXPLAIN ANALYZE` to show how an index reduces disk reads from thousands of pages to just a handful.

The guide uses practical examples, creating a table with a million rows to show a sequential scan taking 265ms versus an index scan at 0.077ms. It details the six default index types and mentions extensions. A key insight is that indexes only help when queries return less than 15-20% of a table; otherwise, a sequential scan may be more efficient, guided by the planner's statistics.

Developers should consider their query patterns before adding indexes, as they consume storage—in the example, the index matched the table's 30MB size. The article advises refactoring queries or using summary tables for large result sets instead of defaulting to indexing. Future topics could explore advanced index options for specific use cases, a common need for optimizing real-world database performance.