Primary and Foreign keys

Hi, I've been trying to understand if there is any performance benefit in using primary and foreign key constraints when performing join queries. I've tested joining a table with 1 million rows with one with 60k. Tryed the same queries with and without constraints and couldn't see a significant change in execution time. The tables are not that big but they are a sample of what we'll be working with in average. Should i be seeing any difference? Hows do PK and FK constraints affect query performance in Monetdb? Will it only be noticeable with larger datasets? Thank you Hilario Fernandes