A million records would do fine with mysql 😉 Depending on what it contains, of course. If it is huge binaries or large amounts of text, you may experience some performance decrease. And the larger the db, the longer time for searching through it - especially with search in text.
Just remember to set the int's to enough length.
[edit]Just mentioning: never tried with so many records. I'm usually satisfied with a user or two, and a few hundred rec's 😉 [/edit]
knutm