BPEL Partnerlinks thoughts

Today I have a support session with a colleague. One of the questions he came up with was about BPEL-partnerlinks. In his current project they have BPEL Partnerlinks to integrate with Pl/Sql procedures on E-Business Suite. They tend to introduce a partnerlink for every invoke of a Pl/Sql procedure. So how about reuse of partnerlinks?

Well at first thought the answer is simple: there is no one-to-one relationship between a partnerlink and invokes of that partnerlink. So you can introduce as many invokes on a certain partnerlink as you want.
However at second thought there are a few considerations. I'll give a few that I came up with:

• Invokes preferably are done in seperate scopes. That is: I prefer to do so. That provides the possibility to catch exceptions on that scope specifically. Variables are kept local as much as possible. Escpecially when the documents they hold can be large. At least you should think about the scope of variables. So if the invoke's input and output variabables are locally declared then they cannot be reused amongst invokes.
• If the input and output variables of the invokes are local and thus not shared, you need to build them up from scratch. This can introduce extra assign steps that might be avoided when declare the variables in a larger spanning scope. Extra assign activities with copy steps cost time. A little perhaps, but still they do. Shared variables are stored to dehydration store over and over again.
  
• A shared partnerlink has thus shared MCF (managed connection factory)-properties. And possibly other adapter-related properties. Normally you probably want that. So in most cases it is advisable to share partnerlinks escpecially on adapters. Then you have to configure them only once. However in some cases you might (for instance with queues) use other parameters. Maybe you have two EBS-instances and a process calling the same procedure but on seperate instances. Then you need to split them up of course.
• Be aware of transactions. The database adapter normally uses connection-pooled datasources. Database sessions are shared amongst instances. You might expect (but I won't rely on it!) that if you share a database-adapter-partnerlink (invoke it multiple times) in a synchronous process, that every invoke would use the same database-session. So for instance your application context settings, package variables, etc. are shared. Although I would check on run-time, you can use that for performance purposes. In a synchronous process you may rely on the fact that this occurs in the same database-transaction. However, if you use different partnerlinks for in fact the same Pl/Sql procedure/function call, the chance is large that you get another database-session. BPEL might need to rely on XA-transaction mechanisms. I don't think this is functionally a big problem. But might cause issues on processes with high performance requirements.
• Maintenance: having multple partnerlinks for the same database procedure or even the same purpose introduces extra maintenance cost and a higher risk. I would not expect that a BPEL-project would have multiple partnerlinks for the same purpose. So in a Change Request or Test-Issue I tend to solve/change the first partnerlink and forget about possible others. And why should I be different from fellow developers? A good developer is a lazy one...
  Input and Output variables are based on the message-definitions of the partnerlinks-wsdl's. So changing one partnerlink might change the message definitions. If you reuse your partnerlinks, changing them will effect all the related variables.
  

These are thoughts that crossed my mind in thinking it over. To be sure you need to check by testing. But I do think that in most cases you should declare a partnerlink for a certain purpose only once. In principle that's the best practice. And that will prevent a lot of possible issues. Only re-declare a partnerlink if you have good reasons for it.