[hibernate-dev] new proposal for tx timeout handling using transaction DISASSOCIATING event notification...

[Scott Marlow]

On 03/10/2015 11:44 AM, Steve Ebersole wrote:
> Scott, I am not following.  Pardon me if I am being dense :)
>
> Today, in our afterCompletion hooks we have code that, in the case of
> rollback, tries to make a determination of whether the rollback is due
> to a timeout or a "normal" rollback.  If we deem a timeout occurred,
> then we delay the afterCompletion processing.

Currently, in our afterCompletion hooks, the determining code isn't 
aware of the current/last application thread id.  I think that we are 
only tracking the first thread id that is used with the Hibernate 
session but not the last thread id.

>
> So how, specifically, would this be different in what you propose?

The new approach will not use thread id, instead in our afterCompletion 
call, we will have the TM level knowledge, of whether the application 
thread has called tx rollback/suspend/commit yet.  If the application 
thread has called tx rollback/suspend/commit already, the 
afterCompletion call can safely clear managed entities from the session 
without violating concurrency concerns.  If the application has not yet 
called tx rollback/suspend/commit yet, we need to defer the clearing of 
the Hibernate session, until the TM listener calls us back, to let us 
know that the application has called tx rollback/suspend/commit, at 
which time we can safely clear the Hibernate session without violating 
(Hibernate session) concurrency concerns.

>
> Are you saying that with this listener approach, that the listener would
> be notified of disassociation prior to the afterCompletion callback on
> our RegisteredSynchronization?  But in the timeout case, the
> disassociation would happen later?

Yes.  It is also possible that in the timeout case, that the 
disassociation will come first (e.g. if there is a race between the app 
committing the transaction and the reaper thread timing out) but more 
likely that the disassociation comes later for the timeout case.

FYI, the TM level SPI changes [4][5] are still open for review.

Scott

[4] https://github.com/jbosstm/jboss-transaction-spi/pull/5
[5] https://github.com/jbosstm/narayana/pull/810

>
> On Mon, Mar 9, 2015 at 1:19 PM, Scott Marlow <smarlow at redhat.com
> <mailto:smarlow at redhat.com>> wrote:
>
>     With a proposed TM level listener, we will have an SPI for notification
>     of when application threads associated with a JTA transaction, become
>     disassociated with the transaction (tm.commit/rollback/suspend time).
>     Having this knowledge in a synchronization callback, can determine
>     whether the persistence context should be cleared directly from the
>     Synchronization.afterCompletion(int) call or should be deferred until
>     the transaction is disassociated from the JTA transaction.
>
>     This idea is based on a TM level listener approach that Tom Jenkinson
>     [1] suggested.  Mike Musgrove has a "proof of concept" implementation of
>     the suggested changes [2].  I did some testing with [3] to see if the
>     improvement helps with clearing entities that might still be in the
>     persistence context after a background tx timeout.
>
>     I'm wondering if in the Hibernate ORM
>     Synchronization.afterCompletion(int status) implementation, in case of
>     tx rollback, if we could defer the clearing of the Hibernate session to
>     be handled by the JtaPlatform.  This could be setup at
>     EntityManager.joinTransaction() time (if a new property like
>     "hibernate.transaction.defer_clear_session" is true).  Perhaps via a
>     JtaPlatform.joinTransaction(EntityManager) registration call?
>
>     Thoughts?
>
>     Scott
>
>     [1] https://developer.jboss.org/thread/252572?start=45&tstart=0
>
>     [2]
>     https://github.com/mmusgrov/jboss-transaction-spi/blob/threadDisassociationListener/src/main/java/org/jboss/tm/
>
>     [3]
>     https://github.com/scottmarlow/wildfly/tree/transactiontimeout_clientut_noejb_wildfly9_march5_2015
>
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