----- Original Message -----
> From: "Marek Libra" <mlibra@redhat.com>
> To: "Martin Perina" <mperina@redhat.com>
> Cc: "Piotr Kliczewski" <pkliczew@redhat.com>, "Michal Skrivanek" <mskrivan@redhat.com>, "engine-devel@ovirt.org"
> <devel@ovirt.org>

> Sent: Wednesday, November 25, 2015 5:19:31 PM
> Subject: Re: [ovirt-devel] Push notifications in 4.0 backend
>
>
>
> ----- Original Message -----
> > From: "Martin Perina" <mperina@redhat.com>
> > To: "Eli Mesika" <emesika@redhat.com>
> > Cc: "Piotr Kliczewski" <pkliczew@redhat.com>, "engine-devel@ovirt.org"
> > <devel@ovirt.org>, "Michal Skrivanek"
> > <mskrivan@redhat.com>
> > Sent: Wednesday, 25 November, 2015 11:20:49 AM
> > Subject: Re: [ovirt-devel] Push notifications in 4.0 backend
> >
> >
> >
> > ----- Original Message -----
> > > From: "Eli Mesika" <emesika@redhat.com>
> > > To: "Vojtech Szocs" <vszocs@redhat.com>
> > > Cc: "Piotr Kliczewski" <pkliczew@redhat.com>, "Michal Skrivanek"
> > > <mskrivan@redhat.com>, "engine-devel@ovirt.org"
> > > <devel@ovirt.org>
> > > Sent: Wednesday, November 25, 2015 10:42:35 AM
> > > Subject: Re: [ovirt-devel] Push notifications in 4.0 backend
> > >
> > >
> > >
> > > ----- Original Message -----
> > > > From: "Vojtech Szocs" <vszocs@redhat.com>
> > > > To: "Martin Betak" <mbetak@redhat.com>
> > > > Cc: "engine-devel@ovirt.org" <devel@ovirt.org>, "Piotr Kliczewski"
> > > > <pkliczew@redhat.com>, "Michal Skrivanek"
> > > > <mskrivan@redhat.com>
> > > > Sent: Monday, November 23, 2015 6:22:45 PM
> > > > Subject: Re: [ovirt-devel] Push notifications in 4.0 backend
> > > >
> > > >
> > > >
> > > > ----- Original Message -----
> > > > > From: "Martin Betak" <mbetak@redhat.com>
> > > > > To: "Vojtech Szocs" <vszocs@redhat.com>
> > > > > Cc: "Einav Cohen" <ecohen@redhat.com>, "engine-devel@ovirt.org"
> > > > > <devel@ovirt.org>, "Roy Golan" <rgolan@redhat.com>,
> > > > > "Roman Mohr" <rmohr@redhat.com>, "Michal Skrivanek"
> > > > > <mskrivan@redhat.com>,
> > > > > "Piotr Kliczewski" <pkliczew@redhat.com>,
> > > > > "Tomas Jelinek" <tjelinek@redhat.com>, "Alexander Wels"
> > > > > <awels@redhat.com>,
> > > > > "Greg Sheremeta" <gshereme@redhat.com>,
> > > > > "Scott Dickerson" <sdickers@redhat.com>, "Arik Hadas"
> > > > > <ahadas@redhat.com>,
> > > > > "Allon Mureinik" <amureini@redhat.com>,
> > > > > "Shmuel Melamud" <smelamud@redhat.com>, "Jakub Niedermertl"
> > > > > <jniederm@redhat.com>, "Marek Libra"
> > > > > <mlibra@redhat.com>, "Martin Perina" <mperina@redhat.com>, "Alona
> > > > > Kaplan"
> > > > > <alkaplan@redhat.com>, "Martin Mucha"
> > > > > <mmucha@redhat.com>
> > > > > Sent: Thursday, November 19, 2015 1:53:07 PM
> > > > > Subject: Re: Push notifications in 4.0 backend
> > > > >
> > > > > Hi All,
> > > > >
> > > > > I have created a PoC patch [1] demonstrating the idea of annotating
> > > > > basic CRUD commands to publish CDI events. It is not meant as 100%
> > > > > solution, but as a simplification of the common use cases when
> > > > > one would inject CDI event with given qualifier and fire it after
> > > > > successful completion of transaction.
> > > >
> > > > The patches (mentioned below) look interesting.
> > > >
> > > > At this point, it would be great if backend core maintainers
> > > > voiced their opinions on the general idea of firing CDI events
> > > > in response to important actions happening on Engine, such as
> > > > backend commands being executed. So, what do you think guys?
> > >
> > > +1
> > >
> > > I am for it, I think it may reduce load from our DB
> >
> > +1
> >
> The load reduction can be achieved and seems like not a big deal to implement
> it.
> +1

Yes, the DB load reduction is perhaps the bigest boon of this effort :-).

My first patch makes very convenient to fire notification from basic CRUD management
operations that manipulate main business entities. The next (and probably more
complicated) step will be a refactoring of the monitoring code to support CDI
(injections and events) and have it fire events of VmDynamic payload. Then on
the event we can have listening scheduler (balancing), HA, ... and other parts
that not only won't have to issue expensive DB queries (e.g. GetVmsRunningOnVds)
but also can be more decoupled from monitoring (e.g. VdsEventListener).

But this will be a little bit more involved than just annotating all CRUD commands
with one annotation :-)

>
> > >
> > > >
> > > > >
> > > > > The usage of this annotations is demonstrated on several basic CRUD
> > > > > commands in [2] on StoragePool, VDS, VDSGroup, .etc
> > > > >
> > > > > As always, comments and suggestions are very welcome!
> > > > >
> > > > > Thank you and best regards,
> > > > >
> > > > > Martin
> > > > >
> > > > > [1] infra: https://gerrit.ovirt.org/#/c/48696/
> > > > > [2] usage: https://gerrit.ovirt.org/#/c/48697/
> > > > >
> > > > >
> > > > >
> > > > > ----- Original Message -----
> > > > > > From: "Vojtech Szocs" <vszocs@redhat.com>
> > > > > > To: "Martin Betak" <mbetak@redhat.com>, "Einav Cohen"
> > > > > > <ecohen@redhat.com>
> > > > > > Cc: "engine-devel@ovirt.org" <devel@ovirt.org>, "Roy Golan"
> > > > > > <rgolan@redhat.com>, "Roman Mohr" <rmohr@redhat.com>,
> > > > > > "Michal Skrivanek" <mskrivan@redhat.com>, "Piotr Kliczewski"
> > > > > > <pkliczew@redhat.com>, "Tomas Jelinek"
> > > > > > <tjelinek@redhat.com>, "Alexander Wels" <awels@redhat.com>, "Greg
> > > > > > Sheremeta" <gshereme@redhat.com>, "Scott
> > > > > > Dickerson" <sdickers@redhat.com>
> > > > > > Sent: Friday, November 13, 2015 9:31:45 PM
> > > > > > Subject: Re: Push notifications in 4.0 backend
> > > > > >
> > > > > > Hi everyone,
> > > > > >
> > > > > > assuming that 4.0 UI will be based on the existing GWT technology,
> > > > > > I'd like to improve two things which I believe are very important:
> > > > > >
> > > > > > #1 goal: improve GWT compilation times
> > > > > >    - don't use standard GWT i18n mechanism which yields separate
> > > > > >      permutation vector, but use our own i18n mechanism instead
> > > > > >    - in practice, compiling for X browsers and Y languages should
> > > > > >      result in GWT compiler processing X permutations (not X * Y)
> > > > > >    - this will also directly impact GWT debug performance, making
> > > > > >      GWT debugging experience less painful for developers
> > > > > >
> > > > > > #2 goal: improve UX related to backend operations
> > > > > >    - replace periodic polling with push notifications that inform
> > > > > >      UI of changes in oVirt "system" as they happen
> > > > > >    - in practice, UI becomes reactive instead of proactive, which
> > > > > >      has several benefits (reduced HTTP load on Engine being the
> > > > > >      most obvious one)
> > > > > >
> > > > > > So what Martin wrote in email below directly relates to #2 goal.
> > > > > >
> > > > > > Push notifications improve user experience regardless of specific
> > > > > > UI technology, regardless of whether we improve existing REST API
> > > > > > (e.g. introduce data aggregations) or not.
> > > > > >
> > > > > > For me, it's a big +1.
> > > > > >
> > > > > > Having BLL commands firing CDI events upon execution makes sense.
> > > > > > That said, I'd suggest to start with a simple implementation and
> > > > > > proceed from there.
> > > > > >
> > > > > > What Martin suggested:
> > > > > >
> > > > > >   void onVmChanged(@Observes @Updated VM vm)
> > > > > >
> > > > > > could be even simplified into:
> > > > > >
> > > > > >   void onCommandExecuted(@Observes @CommandExecuted UpdateVmCommand
> > > > > >   cmd)
> > > > > >
> > > > > > and still it would bring value to the general idea, which is the
> > > > > > ability to detect changes in oVirt "system" as they happen along
> > > > > > with the ability to react upon such changes.
> > > > > >
> > > > > > I'm interested what Engine backend maintainers' thoughts are.
> > > > > >
> > > > > > Regards,
> > > > > > Vojtech
> > > > > >
> > > > > >
> > > > > > ----- Original Message -----
> > > > > > > From: "Martin Betak" <mbetak@redhat.com>
> > > > > > > To: "engine-devel@ovirt.org" <devel@ovirt.org>
> > > > > > > Cc: "Roy Golan" <rgolan@redhat.com>, "Roman Mohr"
> > > > > > > <rmohr@redhat.com>,
> > > > > > > "Michal Skrivanek" <mskrivan@redhat.com>,
> > > > > > > "Piotr Kliczewski" <pkliczew@redhat.com>, "Vojtech Szocs"
> > > > > > > <vszocs@redhat.com>, "Tomas Jelinek" <tjelinek@redhat.com>
> > > > > > > Sent: Wednesday, November 11, 2015 4:34:11 PM
> > > > > > > Subject: Push notifications in 4.0 backend
> > > > > > >
> > > > > > > Hi All,
> > > > > > >
> > > > > > > I would like to take this opportunity to start a discussion
> > > > > > > about the possibility of implementing a user facing change
> > > > > > > notifications.
> > > > > > >
> > > > > > > The benefit of this would be to remove the need for periodic
> > > > > > > polling
> > > > > > > from frontends and other services that consume our REST API.
> > > > > > >
> > > > > > > Also implmenting a common infrastructure on the backend for event
> > > > > > > notifications (e.g. CDI events) would further reduce the internal
> > > > > > > need for polling the DB by the backend itself, maybe even
> > > > > > > reducing
> > > > > > > the need to use DB for some things and just keep them in memory
> > > > > > > and
> > > > > > > updated by CDI event observers.
> > > > > > >
> > > > > > > There are many solutions how to provide the user-facing part of
> > > > > > > the
> > > > > > > notifications:
> > > > > > > Doctor Rest, MQTT, websocket, server-sent events, ... .  Ideally
> > > > > > > these
> > > > > > > notifications
> > > > > > > should be consumable both by web browser (webadmin/userportal)
> > > > > > > but
> > > > > > > also
> > > > > > > by
> > > > > > > other services (such as ManageIQ), or other REST clients such as
> > > > > > > moVirt
> > > > > > > android client.
> > > > > > >
> > > > > > > But regardless of the chosen user-facing transport, I believe a
> > > > > > > common
> > > > > > > infrastructure
> > > > > > > can be implemented on the BLL layer with the usage of CDI events
> > > > > > > fired
> > > > > > > from
> > > > > > > commands.
> > > > > > > I see 2 major sources of changes in the engine (please correct me
> > > > > > > if
> > > > > > > this
> > > > > > > is
> > > > > > > wrong):
> > > > > > > 1) CRUD & management commands
> > > > > > > 2) Vms/Hosts monitoring
> > > > > > >
> > > > > > > the changes originating from 2) are AFAIK very localized and not
> > > > > > > so
> > > > > > > numerous
> > > > > > > so a manual
> > > > > > > firing of appropriate events for VMs and Hosts could be added
> > > > > > > here.
> > > > > > >
> > > > > > > The 1) case is more extensive in terms of required code changes.
> > > > > > > While
> > > > > > > a
> > > > > > > manual solution
> > > > > > > would still be feasible, I believe there is place for a more
> > > > > > > automated/declarative way.
> > > > > > >
> > > > > > > One solution for 1) that comes to my mind are simple
> > > > > > > command-level
> > > > > > > annotations covering the
> > > > > > > Created, Updated, Removed (C, U, and D from CRUD) cases. The goal
> > > > > > > here
> > > > > > > is
> > > > > > > to
> > > > > > > fire the
> > > > > > > appropriate CDI events when an entity is created/updated/deleted.
> > > > > > > Since
> > > > > > > commands usually
> > > > > > > contain getters for entities they work with (such as getVm(),
> > > > > > > getVds(),
> > > > > > > getStorageDomain() ...)
> > > > > > > It should be sufficient for the most common simple cases (of
> > > > > > > course
> > > > > > > this
> > > > > > > will
> > > > > > > not cover
> > > > > > > everything) to use annotation @Creates, @Updates, @Removes on the
> > > > > > > commands
> > > > > > > classes, where
> > > > > > > parameters of the annotation should specify the getter method
> > > > > > > that
> > > > > > > returns
> > > > > > > the affected entity
> > > > > > > (VM/VDS/StorageDomain...). This could be specified by the entity
> > > > > > > class
> > > > > > > token
> > > > > > > or method name
> > > > > > > (depending on the level of "magic" one prefers :-) and the
> > > > > > > CommandBase
> > > > > > > infrastructure would
> > > > > > > then collect those annotations and upon successful completion of
> > > > > > > the
> > > > > > > command
> > > > > > > fire the
> > > > > > > appropriate events.
> > > > > > >
> > > > > > > Example #1:
> > > > > > > @Updates('getVm') // or @Updates(VM.class)?
> > > > > > > public class UpdateVmCommand<...>  extends VmManagementComandBase
> > > > > > > ...
> > > > > > >
> > > > > > > Note that since Java 8 we have repeatable annotations so we can
> > > > > > > have
> > > > > > > more
> > > > > > > complex commands
> > > > > > > that affect more entities.
> > > > > > >
> > > > > > > Example #2:
> > > > > > > @Updates(Vm.class)
> > > > > > > @Updates(VmTemplate.class)
> > > > > > > // possibly also some @Creates and @Removes annotations or their
> > > > > > > combination
> > > > > > > public class ContrivedExampleCommand extends SomeCommandBase
> > > > > > >
> > > > > > > the infrastructure would then look upon successful completion of
> > > > > > > the
> > > > > > > command
> > > > > > > on the getVm()
> > > > > > > and getVmTemplate() methods, invoke them, determine the resulting
> > > > > > > types
> > > > > > > of
> > > > > > > entities VM and VmTemplate
> > > > > > > and since the annotations used were @Updates fire CDI event
> > > > > > > equivalent
> > > > > > > to
> > > > > > >
> > > > > > >   @Inject
> > > > > > >   @Updated // our custom CDI qualifier
> > > > > > >   Event<VM> vmChangedEvent;
> > > > > > >
> > > > > > > and anologously for VmTemplate.
> > > > > > >
> > > > > > > But regardless of the exact implementation of the CDI event
> > > > > > > firing:
> > > > > > > whether
> > > > > > > manual, the above
> > > > > > > proposal, or some crazy usage of AspectJ - the interface for the
> > > > > > > rest
> > > > > > > of
> > > > > > > the
> > > > > > > code should always
> > > > > > > be the like this:
> > > > > > >
> > > > > > > public void onVmChanged(@Observes @Updated VM vm) {
> > > > > > >     // ....
> > > > > > > }
> > > > > > >
> > > > > > > On top of this, I believe, we can build the user-facing part of
> > > > > > > push
> > > > > > > notifications and also
> > > > > > > improve our existing backend code.
> > > > > > >
> > > > > > > Thank you for reading this long email and I welcome any comments
> > > > > > > or
> > > > > > > counter-proposals you
> > > > > > > might have on this topic :-)
> > > > > > >
> > > > > > > Best regards,
> > > > > > >
> > > > > > > Martin
> > > > > > >
> > > > > >
> > > > >
> > > > _______________________________________________
> > > > Devel mailing list
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