eval {
     #table A
     foreach line (...) {
           prepare, execute, commit
     }
    
     #table B
     prepare, execute, commit
}
if ( $@ ) {
    rollback;
}

##</code><code>##

eval {
     #table A
     foreach line (...) {
           prepare, execute
     }
    
     #table B
     prepare, execute 
}
if ( $@ ) {
    rollback
}
else {
    commit;
}