[hibernate-dev] Lambda usage to run a code block in an isolated transaction

[Steve Ebersole]

Most transaction systems do not support nested transactions


On Wed, Sep 14, 2016 at 3:13 PM Sanne Grinovero <sanne at hibernate.org> wrote:

> On 14 September 2016 at 21:02, Steve Ebersole <steve at hibernate.org> wrote:
> > Also, why do you keep defining this in terms of Session, rather than
> > SessionFactory?
>
> I mentioned that same doubt in my first email of this thread.
> I think I prefer Session as that's what people interact with most of
> the time, and it's a better choice if we opt to make this a nested
> transaction of the current one; if it's meant to be totally
> independent yes then we should probably consider the SF.
>
> >
> >
> > On Wed, Sep 14, 2016 at 3:01 PM Steve Ebersole <steve at hibernate.org>
> wrote:
> >>
> >> "Better" according to whom? ;)
> >>
> >> I personally very much dislike the kind of API explosion this kind of
> >> thing leads to.
> >>
> >>
> >> On Wed, Sep 14, 2016 at 2:59 PM Sanne Grinovero <sanne at hibernate.org>
> >> wrote:
> >>>
> >>> On 14 September 2016 at 20:32, Steve Ebersole <steve at hibernate.org>
> >>> wrote:
> >>> > The problem with "execute in isolation" here is that the "isolation"
> >>> > aspect
> >>> > refers to being isolated from any current transaction.  It says
> nothing
> >>> > about whether that stuff-to-execute should itself be transacted.
> This
> >>> > is
> >>> > why, for example, you see IsolationDelegate accept a `transacted`
> >>> > boolean
> >>> > argument.
> >>> >
> >>> > How would you propose we pass such a flag in this case?  Or are you
> >>> > proposing that this always start a (new) transaction?
> >>>
> >>> I had only the (new) transaction case in mind, but sure you could add
> >>> a `transacted` boolean parameter.
> >>>
> >>> Or we make it explicit with a better method name:
> >>>
> >>> s.executeInSubtransaction( session -> session.save(...) );
> >>>
> >>> Thanks,
> >>> Sanne
> >>>
> >>>
> >>> >
> >>> > On Wed, Sep 14, 2016 at 1:39 PM Sanne Grinovero <sanne at hibernate.org
> >
> >>> > wrote:
> >>> >>
> >>> >> Today porting some benchmark code to Hibernate ORM 5.2 I had several
> >>> >> difficulties around the fact that the code now needs to be different
> >>> >> depending on transactions being container managed or not.
> >>> >>
> >>> >> My goal was to have a single benchmark test which I could compile
> once
> >>> >> and run in either JavaSE or CMT; with some help from Steve I figured
> >>> >> the necessary incantations out but ... it looks very unpractical.
> >>> >>
> >>> >> One way is to use an isolation delegate, which looks like this:
> >>> >>
> >>> >> final SessionImplementor session = (SessionImplementor) s;
> >>> >>
> >>> >>
> >>> >>
> session.getTransactionCoordinator().createIsolationDelegate().delegateWork(
> >>> >>    new WorkExecutorVisitable() {
> >>> >>       @ Override
> >>> >>       public Object accept(WorkExecutor executor, Connection
> >>> >> connection) throws SQLException {
> >>> >>          /// Some work with PreparedStatement on Connection..
> >>> >>       }
> >>> >> }, true );
> >>> >>
> >>> >> This worked fine for some raw SQL used for the benchmark
> >>> >> initialization, but in another case I'd prefer to use the Session
> API
> >>> >> rather than dealing with PreparedStatements and native connections;
> >>> >> it looks like we don't have an equivalent "run code in isolation"
> for
> >>> >> the Session ?
> >>> >>
> >>> >> It would be great if I could just pass a lambda to a Session and
> have
> >>> >> this executed on a "child Session" in the scope of a "child
> >>> >> Transaction", or just start and commit a transaction if there isn't
> >>> >> one.
> >>> >>
> >>> >> s.executeInIsolation( session -> session.save(...) );
> >>> >>
> >>> >> So I'd expect that details like how to begin the transaction, how it
> >>> >> should be committed (or rolled back in case of exceptions), how to
> >>> >> lookup a TransactionManager, and especially how to not leak
> resources
> >>> >> should be handled for the user.
> >>> >>
> >>> >> Obviously the inner Session instance is a different one than the
> >>> >> outer, so any data returned by this block should be considered
> >>> >> detached; maybe this limitation would be clearer if the method was
> >>> >> hosted on SessionFactory or StatelessSession instead?
> >>> >> Although it wouldn't necessarily have the limitations of a
> >>> >> StalessSession, and it would be nice to have the inner transaction
> >>> >> behave as a nested one when there's already one in the host Session.
> >>> >>
> >>> >> Looking forward for comments and improvement ideas :)
> >>> >>
> >>> >> Thanks,
> >>> >> Sanne
> >>> >> _______________________________________________
> >>> >> hibernate-dev mailing list
> >>> >> hibernate-dev at lists.jboss.org
> >>> >> https://lists.jboss.org/mailman/listinfo/hibernate-dev
>