[ovirt-devel] hibernate's internal PersistentBag sent to FE

Tue Jun 2 07:05:11 UTC 2015

----- Original Message -----
> From: "Tomas Jelinek" <tjelinek at redhat.com>
> To: "Oved Ourfali" <ovedo at redhat.com>
> Cc: awels at redhat.com, "Liran Zelkha" <lzelkha at redhat.com>, devel at ovirt.org
> Sent: Tuesday, June 2, 2015 9:59:17 AM
> Subject: Re: [ovirt-devel] hibernate's internal PersistentBag sent to FE
> 
> 
> 
> ----- Original Message -----
> > From: "Oved Ourfali" <ovedo at redhat.com>
> > To: awels at redhat.com
> > Cc: "Liran Zelkha" <lzelkha at redhat.com>, devel at ovirt.org
> > Sent: Tuesday, June 2, 2015 8:35:56 AM
> > Subject: Re: [ovirt-devel] hibernate's internal PersistentBag sent to FE
> > 
> > top-posting:
> > Due to the fact that we'll see that all over the place, I really think that
> > it would be best to support that at the frontend level, and not the backend
> > level.
> 
> well, from philosophical perspective I think that sending
> org.hibernate.collection.**internal**.PersistentBag from backend to FE and
> than faking it's implementation on FE
> is a way to hell. It will bring lots of problems. For example the FE will be
> directly dependent on the internal structure of an internal hibernate class
> and if we update hibernate, FE can fail miserably.
> Also the FE patch (https://gerrit.ovirt.org/#/c/41682/1) seems to be more
> tricky than expected - it seems to be working but Omer had issues with it
> and in some cases (when the delegating also retainAll()) it caused my JRE to
> fail on SIGSEGV.
> It can be fixed on FE but it is a hack with all risks this kinds of hacks
> brings.

I don't think it really matters where we do it, as long as server code will still use the PersistentBag (otherwise we won't be able to use attached entities, and performance will suffer). 
I believe that serializing these objects to JSON/XML - will work, we won't need to do 2 level of conversions (PersistentBag-->List-->JSON/XML).
So if the issue is only on the GWT side, and we won't to write this code once, and not per entity - where is the best way to put it?

> 
> > Doing it in the backend level will cause a lot of overhead.
> 
> Is it really lots of overhead? Comparing to all other layers the data has to
> pass anyway? When abandoning GWT FE and start to use REST we will anyway
> remove the GenericApiGWTServiceImpl which contains this cleaning
> (https://gerrit.ovirt.org/#/c/41810/).
> 
> > I'll leave the technical details to the UX experts here to see what's the
> > right approach to do it in the frontend side.
> > 
> > Thanks,
> > Oved
> > 
> > ----- Original Message -----
> > > From: "Alexander Wels" <awels at redhat.com>
> > > To: "Martin Perina" <mperina at redhat.com>
> > > Cc: "Liran Zelkha" <lzelkha at redhat.com>, devel at ovirt.org
> > > Sent: Tuesday, June 2, 2015 4:16:31 AM
> > > Subject: Re: [ovirt-devel] hibernate's internal PersistentBag sent to FE
> > > 
> > > On Monday, June 01, 2015 10:51:28 AM Martin Perina wrote:
> > > > ----- Original Message -----
> > > > 
> > > > > From: "Alexander Wels" <awels at redhat.com>
> > > > > To: "Tomas Jelinek" <tjelinek at redhat.com>
> > > > > Cc: "Liran Zelkha" <lzelkha at redhat.com>, devel at ovirt.org
> > > > > Sent: Monday, June 1, 2015 4:19:47 PM
> > > > > Subject: Re: [ovirt-devel] hibernate's internal PersistentBag sent to
> > > > > FE
> > > > > 
> > > > > On Monday, June 01, 2015 09:33:07 AM Tomas Jelinek wrote:
> > > > > > ----- Original Message -----
> > > > > > 
> > > > > > > From: "Alexander Wels" <awels at redhat.com>
> > > > > > > To: devel at ovirt.org
> > > > > > > Cc: "Tomas Jelinek" <tjelinek at redhat.com>, "Liran Zelkha"
> > > > > > > <lzelkha at redhat.com> Sent: Monday, June 1, 2015 3:16:34 PM
> > > > > > > Subject: Re: [ovirt-devel] hibernate's internal PersistentBag
> > > > > > > sent
> > > > > > > to
> > > > > > > FE
> > > > > > > 
> > > > > > > On Monday, June 01, 2015 09:08:50 AM Tomas Jelinek wrote:
> > > > > > > > Hey all,
> > > > > > > > 
> > > > > > > > since the org.ovirt.engine.core.common.job.Job/Step... has been
> > > > > > > > moved
> > > > > > > > to
> > > > > > > > use
> > > > > > > > the JPA we have a problem on frontend. The problem is that the
> > > > > > > > @OneToMany
> > > > > > > > annotations results in a List which is of type PersistentBag.
> > > > > > > > When
> > > > > > > > we
> > > > > > > > send
> > > > > > > > this to Frontend it fails during deserialization. It actually
> > > > > > > > fails
> > > > > > > > quite
> > > > > > > > bad because the FE already has an ui-override of it which is
> > > > > > > > not
> > > > > > > > correct
> > > > > > > > resulting in a ton of NPEs in development mode.
> > > > > > > > 
> > > > > > > > So, there are 2 nasty fixes I have made where none of them
> > > > > > > > should
> > > > > > > > be
> > > > > > > > merged
> > > > > > > > but demonstrate the possibilities: 1: extend the FE to be able
> > > > > > > > to
> > > > > > > > work
> > > > > > > > with
> > > > > > > > the PersistentBag (https://gerrit.ovirt.org/#/c/41682/) not
> > > > > > > > really
> > > > > > > > good
> > > > > > > > solution since the PersistenBag is an internal Hibernate class
> > > > > > > > which
> > > > > > > > is
> > > > > > > > really not meant to be passed around
> > > > > > > > 
> > > > > > > > 2: fix on the backend to not send the PersistentBag but an
> > > > > > > > ArrayList.
> > > > > > > > This
> > > > > > > > is only a PoC fixed on a command we face the problem
> > > > > > > > (https://gerrit.ovirt.org/#/c/41797/) Obviously this is not
> > > > > > > > going
> > > > > > > > to
> > > > > > > > work
> > > > > > > > for other commands accessing the same Job nor for other
> > > > > > > > entities.
> > > > > > > > 
> > > > > > > > So, the first option is generic but very very bad. The second
> > > > > > > > option
> > > > > > > > should
> > > > > > > > be used but not sure how to do this in a cheep way (e.g.
> > > > > > > > without
> > > > > > > > using
> > > > > > > > reflection to deep traverse everything sent back to frontend
> > > > > > > > checking
> > > > > > > > if
> > > > > > > > it
> > > > > > > > does not have a PersistentBag in it.
> > > > > > > 
> > > > > > > Tomas,
> > > > > > > 
> > > > > > > Thanks, I was investigating the same issue, I noticed it last
> > > > > > > Friday
> > > > > > > just
> > > > > > > before leaving, so I was investigating the problem to see what
> > > > > > > was
> > > > > > > going
> > > > > > > on. You are right we should not be sending PersistentBag to the
> > > > > > > frontend
> > > > > > > at all. So how about we do a combination of [1] and [2], but
> > > > > > > instead
> > > > > > > of
> > > > > > > delegating in [1] we actually simple throw an exception stating
> > > > > > > don't
> > > > > > > sent PersistentBag to the front end. that way anyone
> > > > > > > inadvertently
> > > > > > > using
> > > > > > > it will be notified immediately (since their code won't work).
> > > > > > 
> > > > > > Throwing the exception would help us in debugging but the main
> > > > > > question
> > > > > > is
> > > > > > how will we make it work? Since we are planning to move more and
> > > > > > more
> > > > > > to
> > > > > > JPA so we will face this issue more and more often. Solving it one
> > > > > > by
> > > > > > one
> > > > > > on backend in each command is not going to work.
> > > > > 
> > > > > How about something like this [1]? It appears to use some aspects to
> > > > > translate
> > > > > the hibernate internal classes into normal java util classes.
> > > > > 
> > > > > [1] https://code.google.com/p/dehibernator/
> > > > 
> > > > Well, not sure about that from performance point of view.
> > > > 
> > > > If we really move away from GWT completely in 4.0, then implementing
> > > > all
> > > > hibernate inner collections in "uioverride" in a similar way as Tomas
> > > > did
> > > > seems to me as the best solution from performance and "easiest to
> > > > remove
> > > > when not needed" point of view.
> > > > 
> > > 
> > > I took some inspiration from that code and wrote my own fairly simple
> > > hibernate persistent collection replacer, and I put the patch up here
> > > [3].
> > > It
> > > still uses reflection so it is probably not the fastest thing ever
> > > written.
> > > 
> > > [3] https://gerrit.ovirt.org/#/c/41810/
> > > 
> > > > > > > Alexander
> > > > > > > 
> > > > > > > > Any better ideas?
> > > > > > > > Thanx,
> > > > > > > > Tomas
> > > > > > > > _______________________________________________
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> > > > > > > > Devel at ovirt.org
> > > > > > > > http://lists.ovirt.org/mailman/listinfo/devel
> > > > > 
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