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

Question

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?