title: Scaling with kettle, concurrency issues
body: <p>I pretend to scale my app and some part of the process includes to run kettle jobs simultaneously by some processing clients, in some point transformations need to perform combination lookup on some shared table (let's suppose "clients_table"), this table grows quickly due to all possible clients are unknown, so they are inserted as the show up. Combination lookup on simultaneously executing jobs (let's say 2 but could be more than that, each per client) over this table, it is presenting concurrency issues because of "duplicate entry key xxx" error I suppose while inserting non existing clients (when combination lookup didn't find them in the table to retrieves it's id). It's a fact that every time processing clients executes kettle jobs will transfer new clients so above problem it's very common.  I wonder if I'm breaking kettle philosophy or I'm missing something, I've read about making kettle transformations transactional, could that be my solution, because I think what's going on is that combination lookup step isn't transactional?
  Give me some ideas.</p>
  
  <p>PS: I'm using Kettle 4.2 and MySql 5.2</p>