foreach $CPU (@CPUs) {
    
    create dbh for this CPU;
    prepare_cached SELECT;
    prepare_cached INSERT;

    foreach combination { # criterion have affinity with CPU core
                          # so criterion is always unique to CPU
        generate row-data; # 
        check if row already exists; # what the SELECT sth is for
        if not then {
            insert new row; # what the INSERT sth is for
        }
    }
}