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From Edison Su <Edison...@citrix.com>
Subject RE: About Transaction management
Date Fri, 24 Aug 2012 23:11:30 GMT


> -----Original Message-----
> From: Prasanna Santhanam [mailto:prasanna.santhanam@citrix.com]
> Sent: Thursday, August 23, 2012 7:50 AM
> To: CloudStack Dev
> Subject: About Transaction management
> 
> I was looking at moving the Simulator managed entities into a
> different database and found that Transaction.java is not able to
> switch to the right DB based on context of its execution.
> 
> To explain further:
> 
> The ServerResource for simulator which is the bottommost layer manages
> a set of Daos which alter entities in the database : `simulator`. When
> the context goes back to the middle manager layers of CS
> (ResourceManagerImpl say) after a Command is executed at the
> ServerResource all the Daos in the Managers seem to access the
> `simulator` db instead of the `cloud` db for their operations.
> 
> I noticed that Transaction.java holds a threadlocal store where it
> retains the _previously used database.
> 
> 1) Is this a bad design for the simulator in that it tries to alter db
> entities at the ServerResource?
> 2) Or is this a bug in the way transactions are managed?
> 3) Or is this the wrong way to switch databases?

Transaction.java has only one database(cloud) in mind, so if you change the database in transaction,
then need to switch back to cloud.
You will find the following code in usagemanagerImpl all over the place:
    // switch back to CLOUD_DB
                Transaction swap = Transaction.open(Transaction.CLOUD_DB);


>

> txn = Transaction.open(Transaction.SIMULATOR_DB)
> try {
>  	   txn.start();
> 		 .... some persistence code here....
> 		 txn.commit();
> 
> 		} catch (Exception ex) {
> 
> 		  txn.rollback();
> 
> 		} finally {
> 
> 			txn.close();
> 
> 		}
> 
> Thanks,
> 
> --
> Prasanna.,

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