[wildfly-dev] (transaction enlistment for ACID but none for BASE...) update on WildFly NoSQL prototype integration...

[Emmanuel Bernard]

On Mon 2016-07-18 12:20, Scott Marlow wrote:
> Thanks for the feedback.
> 
> On 07/18/2016 09:24 AM, Emmanuel Bernard wrote:
> > I'm lost.
> > 
> > What is the expected code a developer will write ?
> > 
> > If that' something along the lines of:
> > 
> > jta.beginTx() // declaratively or imperatively
> > neo4j.beginTx()
> > ...
> > neo4j.commit()
> > jta.commit() //declaratively or imperatively
> 
> They are not limited to writing the above code.  In addition, the developer
> can also avoid calling neo4j.beginTx()/neo4j.commit(). Something like:
> 
> jta.beginTx() // declaratively or imperatively
> session = driver.session() // internally does session.beginTransaction()
> ...
> jta.commit() //declaratively or imperatively
> 
> The calls to neo4j.beginTx()/commit() are ignored.
> 
> The choice of ignoring those calls, is made against the alternative of
> throwing an exception.  The reason for ignoring the neo4j transactional
> calls, is to be more compatible with existing ne04j code that may be using
> the neo4j transactional code, with the goal that the JTA transaction
> controls the underlying ne04j transaction.  Neo4j transactional code also
> runs the statements against the neo4j transaction class, instead of the
> neo4j session class.

You mean having existing code work with the new JTA transaction net?
I don't think you can safely support that. What if the code does

@Transactional
public void doThings() {
   session = drive.session();
   session.beginTransaction();
   try {
       // do things
   catch (Exception e) {
       // swallow exception because we will fix things
       session.rollback();
       session.beginTransaction();
       // do something else
       session.commit();
    }
}

Such an existing code won't work if JTA in involved and
session.beginTrnasaction() / commit() are ignored.

So only code written with the idea of the JTA net in mind will be safe.

> > 
> > then I find it very user unfriendly to force the code to call both Tx
> > APIs. It should be one or the other.
> 
> Do you really want to rewrite your neo4j code to avoid the neo4j tx APIs
> when enlisted into a JTA transaction?  Or should the neo4j tx API calls be
> ignored when enlisted into a JTA transaction (as we are doing now)?

See my above example of already existing code.

For new code that you want to run both in SE and Wildfly, that's an
interesting question but how would you do it in practice? A try catch
but rethrowing the exception in case JTA is involved and needs to be
notified of the tx rollback?
I'm interested to see concrete code because if doable, it will have lots
of constraints and be limited to very specific patterns of code I think.
But again, let's show each other code.

Emmanuel