Comparing Two Large MySQL Tables

I have two tables, class_current and class_compjar

class_current has 3 fields: package,class,bundle
class_compjar has 3 fields: package,class,compjar_id

they both have about 25k rows

I’d like to find out the differences between them.

I ran a this JOIN query, and it completely froze my machine for several minutes, I had to restart my computer:

SELECT a.class,a.package FROM class_current AS a LEFT JOIN class_compjar AS b ON ( a.class=b.class AND a.package=b.package ) WHERE b.class IS NULL

or something like that, i dont remember the exact query but i’m pretty positive it was this one.

Is there a better way? Could someone point me in the right direction?
Thanx in advance.Comparing Two Large Tables