pgrouting pgr_ksp with large dataset

I have large osm dataset When I execute a pgr_ksp query, it takes +30 minutes

Example: SELECT seq , id1 , id2 , cost FROM pgr_ksp( 'SELECT id, source, target, cost FROM myways', 524356, 1210854, 2, false);

my virtual server has 4 processors and 3GB RAM.

my ways table has 2290470 rows,

The other functions works normally but pgr_ksp not

What is the problem ? or what should I do? Thanks!!!