On Tuesday, June 02, 2015 03:05:11 AM Liran Zelkha wrote:
----- Original Message -----
From: "Tomas Jelinek" <tjelinek@redhat.com> To: "Oved Ourfali" <ovedo@redhat.com> Cc: awels@redhat.com, "Liran Zelkha" <lzelkha@redhat.com>, devel@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@redhat.com> To: awels@redhat.com Cc: "Liran Zelkha" <lzelkha@redhat.com>, devel@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?
The original problem comes from the fact that we are serializing an object from the backend to the frontend that the frontend cannot handle (The persistent bag). This is a backend implementation detail that the frontend really doesn't care about. In essence GWT is Javascript that is made to look like Java, but it has a bunch of limitations due to the fact it still ends up as javascript in the end.
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/).
The overhead comes from having to scan through every single object that we are transferring to the front end, even though right now only one or two object types have this particular problem. The scanning only happens if we actually transfer the object to the frontend. If there was a way to determine if we need to scan the objects being returned to the front end that would cut down on the overhead. Another question to ask, is the overhead BAD enough to care? I honestly don't know without doing some profiling. But my gut is telling me no it is not.
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@redhat.com> To: "Martin Perina" <mperina@redhat.com> Cc: "Liran Zelkha" <lzelkha@redhat.com>, devel@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@redhat.com> To: "Tomas Jelinek" <tjelinek@redhat.com> Cc: "Liran Zelkha" <lzelkha@redhat.com>, devel@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@redhat.com> > > To: devel@ovirt.org > > Cc: "Tomas Jelinek" <tjelinek@redhat.com>, "Liran Zelkha" > > <lzelkha@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.
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 > > > _______________________________________________ > > > Devel mailing list > > > Devel@ovirt.org > > > http://lists.ovirt.org/mailman/listinfo/devel
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