Problem with transactions?

[eluser]Mel [RS][/eluser]
Hi:
I'm developing a project and I've a problem with the transactionability of CI. I'll try to explaint it:

Code:

trans_start();

$id = query_1();

query_2($id);
query_3($id);
query_4($id);
query_5($id);
query_6($id);

trans_end();

My problem is, 'case I've to many users making that work and, the $id var is the same to some users while the transaction is not ended.

So, can you give me some orientation about how to make this? or implements some nested transactionability (I've searched in forums with bad luck).

Thanks in advance.