[jbpm-dev] Help with ht problem? (Re: BZ 853019)

[Maciej Swiderski]

Marco, another way could be to ensure transaction is started when 
taskservicesession is created and closed (committed/rolledback) when 
taskservicesession is disposed, I did that for a fix on 
https://issues.jboss.org/browse/JBPM-3763 which is on postgresql and 
worked fine. So that way we ensure that session.write is in transaction 
as well. Of course not tested all possible cases but worked for main ones.

Wdyt?

Maciej

On 12.09.2012 12:22, Marco Rietveld wrote:
> Hi Maciej and Mauricio,
>
> I'm struggling to find a good solution for a problem and was hoping to 
> get your advice about the following.
>
>
> The human-task service uses it's entities as DTO's, namely the Task 
> class/instances.
>
> However, we use Hibernate, which uses lazy-loading, which means that 
> Hibernate substitutes proxy instances in collections until the actual 
> collection elements are needed.
>
> With Hibernate 3, we miraculously were able to avoid any large 
> problems. However, testing with EAP 6 has uncovered situations, 
> primarily with postgresql, in which this strategy (entity as DTO) just 
> won't work.
>
> The problem is that even if all the "persistence" work is done in one 
> tx, the collections are still lazily-loaded. That means if a task 
> service operation has to return a Task instance, that the 
> serialization of the Task object (when it's being sent) triggers the 
> loading of entities. Due to postgresql's Large Object facility, this 
> means that there needs to be a transaction around this action. Because 
> we don't surround the session.write(resultsCmnd); operation with a tx, 
> we get an exception.
>
> (To tell the truth, I don't understand why this worked with Hibernate 
> 3.. )
>
> As I've been writing this, I've come up with a couple of solutions:
>
> 1. Turn off lazy-loading for all entities.
> 2. Force the loading of all relevant entities by going through the 
> object tree (task.getPeopleAssignments().size(), etc.. )
> 3. Put a transaction around session.write(resultsCmnd);
>
> Option 1 has a big impact on performance, especially if we start 
> talking about high-volumes.
> Option 2 has a slightly larger impact on performance  but Option 3 
> seems a little bit ugly to me.
>
>
> Are there any options I missed? Any advice or comments?
>
> Thanks,
> Marco
>
> PS. This is (IMHO) one of the reasons we need to rewrite human-task. 
> I've been working on a proposal/POC, but the important thing is that 
> certain problems that we have now aren't also present in the rewritten 
> version.
>