RE: [Springframework-developer] OpenSessionInViewFilter ideas

[Norris, T. <tys...@be...>]

Hey folks - any other thoughts on this?

Thanks!
tyson

-----Original Message-----
From: Norris, Tyson=20
Sent: Friday, June 25, 2004 8:21 AM
To: spr...@li...
Subject: RE: [Springframework-developer] OpenSessionInViewFilter ideas

The typical use case for accessing a session after rollback is accessing
read-only data which should be available regardless of any transaction
success or failure.=20

Specifically, we have various data that is used to customize the
navigation framework of our webapp. I won't argue that its not efficient
to look it up with each request, but there is nothing technically wrong
with it.

Currently, the session opened in OpenSessionInViewFilter will be used
within the transaction, which causes problems for rollbacks (and even
commits for some unfortunate enough to use weblogic :). The problem
being that after rollback or commit, the navigation data access fails
because the connection is now defunct.

Yes, our app is currently architected to use certain methods as
transactional units, with all of them using "REQUIRES" propagation (some
EJB, some spring/hibernate). We could potentially avoid this problem by
using "REQUIRES_NEW", and have the filter create a new tx (instead of
just open a session) which will affect the datasource behavior in
regards to the transaction, but this breaks the potential interaction of
many of these methods - there should only be 1 transaction per request.
In this way, you could say it's a "nested tx problem", but only in that
we can't use "true nested tx", and requires_new is not useable for us
either.

Session.clear() would help in the case where the lazy-loading-data is
accessed *after* any transactional behavior, but NOT in the case where
data is accessed *before* the transaction. I would rather not force
specific ordering with regards to transactional methods and
lazy-loading-dependent methods.

Let me know what you think

Tyson


-----Original Message-----
From: James Cook [mailto:jim...@do...]=20
Sent: Friday, June 25, 2004 6:37 AM
To: spr...@li...
Subject: RE: [Springframework-developer] OpenSessionInViewFilter ideas

I was wondering (out loud) if Hibernate's session.clear() couldn't be
used
to "reinitialize" its session for continuing work after a rollback or
exception? I suppose if a rollback invalidates the datasource from
further
activity on certain platforms that it wouldn't matter if Hibernate could
recover on its own.

For many that currently need this feature, I suppose they are
architecting
their application to use SAO methods as their transactional units. If a
rollback occurs, it occurs only in the scope of the SAO method call.
They
would also have to "exercise" their business objects in order to load
lazy
collections in the SAO instead of the web tier.

I don't mean to minimize the goal you are trying to achieve, but what
are
some use cases where a developer needs to reuse a session after a
rollback?
Is this in relation to nested transactions?


> -----Original Message-----
> From: spr...@li...
> [mailto:spr...@li...] On
Behalf
> Of Norris, Tyson
> Sent: Thursday, June 24, 2004 9:04 PM
> To: spr...@li...
> Subject: [Springframework-developer] OpenSessionInViewFilter ideas
>=20
> Hi Folks -
> We have been running into problems with migrating an existing CMT EJB
> application to use OpenSessionInViewFilter, and here are a couple
> thoughts on the subject.
>=20
> The basic problem is that when a session is created, then a
transaction
> is initiated and uses that session, if the transaction rolls back, how
> can we still access the initial session created in the filter?
>=20
> Currently the same session is used after entering the transaction.
This
> is a problem for us using weblogic, since weblogic datasource become
> useless after a transaction rolls back (or commits), but I think this
is
> also general practice for hibernate users to close the session on
> rollback:
> "If you rollback the transaction you should immediately close and
> discard the current session to ensure that Hibernate's internal state
is
> consistent."
>=20
> So, what to do? Would it be desirable to build into
SessionFactoryUtils
> the ability to generate a new session for each new transaction?
>=20
> I have worked around the problem temporarily by "manually" doing this.
> That is, I check for an existing JTA transaction, and if its their,
> register a new synchronization that holds a reference to the session
> opened with the OpenSessionInViewFilter, and the
> TransactionSynchronizationManager's session is unbound. When the
> transaction completes, TransactionSynchronizationManager session is
> re-bound, and non-transactional data access can proceed after the
commit
> or rollback.
>=20
> This of course presents a potential problem of loading the same data
in
> multiple sessions, but this may be negligible for many cases.
>=20
> Is this something worth adding as an additional parameter to
> SessionFactoryUtils.getSession()? When specified (true), if an
existing
> SessionHolder is found, if not already synchronized with a
transaction,
> it would be replaced with a new session, then restored after the
> transaction completes.
>=20
> Let me know what you think. Or if there is a better alternative, I'm
all
> ears :)
>=20
> Thanks
> tyson
>=20
>=20
>=20
>=20
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