For Rails developer

Book High Performance PostgreSQL for Rails.

Here are some good Postgres posts I found for Rails developers.

A Grand Piano for Your Violin

PostgreSQL Performance Considerations

Advanced Postgres Performance Tips

Postgres Index Types

Why Postgres Won't Always Use an Index

Have Some (Referential) Integrity with Foreign Keys

How to Create Postgres Indexes Concurrently in ActiveRecord Migrations

Reading a Postgres EXPLAIN ANALYZE Query Plan

Back to basics: psql