Issue setting FlushMode.COMMIT in Quarkus Hibernate ORM

[leomorgans]

Hi folks,
I'll try to describe an issue we currently have in our project.
For performance purposes we need to set FlushMode as COMMIT in our hibernate Session.
And we realized that this property configuration is not available in application.properties parameters, see: https://quarkus.io/guides/hibernate-orm#hibernate-configuration-properties

So, we took the path to setting up the configuration with persistence.xml file: https://quarkus.io/guides/hibernate-orm#persistence-xml

...
	<persistence-unit name="SomethingPU"	transaction-type="JTA">
		<description>Something Entities</description>
		<properties>
			<!-- Connection specific -->
			<property name="hibernate.dialect" value="org.hibernate.dialect.SQLServer2012Dialect" />
			
			<!-- cache properties -->
			<property name="hibernate.cache.use_second_level_cache" value="true"/>
			<property name="hibernate.cache.use_minimal_puts" value="true"/>
			<property name="hibernate.cache.use_query_cache" value="true"/>
			
			<!-- multitenancy -->
			<property name="hibernate.multiTenancy" value="DATABASE" />
				
			<!-- scan for annotated classes -->
    		       <property name="hibernate.archive.autodetection" value="class"/>
    		
			<!-- performance tunning -->
			<property name="org.hibernate.flushMode" value="COMMIT" />
			<property name="hibernate.jdbc.batch_size" value="100" />
			<property name="hibernate.jdbc.fetch_size" value="400" />
			<property name="hibernate.order_updates" value="true" />
			<property name="hibernate.order_inserts" value="true" />
			<property name="hibernate.max_fetch_depth" value="1" />
			
		</properties>
	</persistence-unit>

When we start our service everything's fine, the properties are loaded into the Session, except for "org.hibernate.flushMode" parameter.
Debugging the code we see this behaviour:

• when the service starts, Quarkus executes the Recorder: io.quarkus.hibernate.orm.runtime.HibernateOrmRecorder
• this class initialize org.hibernate.Session using the class: io.quarkus.hibernate.orm.runtime.TransactionSessions
• TransactionsSessions mantains a Map of io.quarkus.hibernate.orm.runtime.session.TransactionScopedSession
• so, when TransactionScopedSession acquires the Session, it executes:

TransactionScopedSession.aquireSession
line 88:
Session newSession = jtaSessionOpener.openSession();

which ends calling JTASessionOpener.createOptions method:

return sessionFactory.withOptions()
                .autoClose(true) // .owner() is deprecated as well, so it looks like we need to rely on deprecated code...
                .connectionHandlingMode(
                        PhysicalConnectionHandlingMode.DELAYED_ACQUISITION_AND_RELEASE_BEFORE_TRANSACTION_COMPLETION)
                .flushMode(FlushMode.ALWAYS);

Here JTASessionOpener is setting flushMode as ALWAYS
calling the method: SessionFactoryImpl.flushMode

When org.hibernate.internal.SessionImpl is created
org.hibernate.internal.SessionImpl.SessionImpl(SessionFactoryImpl, SessionCreationOptions)
line 266:

if ( getHibernateFlushMode() == null ) {
	final FlushMode initialMode;
	if ( this.properties == null ) {
		initialMode = fastSessionServices.initialSessionFlushMode;
	}
...

The method getHibernateFlushMode() is returning FlushMode.ALWAYS
And because of this, the parameter "org.hibernate.flushMode" from persistence.xml is never setted.

---

We fix this issue setting the flushMode directly in javax.persistence.EntityManager instance, before we use it in any query or DB operation.

But, my questions are:

1. is there a way to bypass JTASessionOpener or use another logic? can it be considered as a bug or issue to solve?
2. is there a better way (than our solution) to fix this issue?
3. is there a plan to add the property "org.hibernate.flushMode" in Quarkus Hibernate ORM extension?, so we can set this in application.properties
   --

Hope the description is clear.
Regards,
Leonel Morgans