Most Postgres performance problems come down to a missing index or a query the planner cannot optimize. You can solve a surprising amount with EXPLAIN ANALYZE and patience.
Read the plan
A sequential scan over a large table on a filtered query is usually a missing index. Add the index, measure again, and let the data guide you rather than guessing.
Index with intent
- Index the columns you filter and join on, not every column.
- Use composite indexes that match your query order.
- Remember that every index slows writes, so remove ones you do not use.
Tune based on measurement, change one thing at a time, and keep a record of what actually moved the needle.