What is the fastest way to fetch the last row from a table?

I have a PostgreSQL table, Prices, with the columns: - price (Decimal) - product_id (Int) There are also created_at and updated_at columns. Prices get updated regularly and I keep old prices in the table. For a given product, the last price in the table is the current price. What is the most efficient way to get the last price for a specific product: - Index product_id and query for the last record - Add a third column active (Boolean) to mark the latest price and create a composite index (product_id and active) - Or something else?