[Engine-devel] Serial Execution of Async Tasks

[Allon Mureinik]

----- Original Message -----
> From: "Allon Mureinik" <amureini at redhat.com>
> To: "Livnat Peer" <lpeer at redhat.com>
> Cc: "Eli Mesika" <emesika at redhat.com>, "Liron Aravot" <laravot at redhat.com>, "Federico Simoncelli"
> <fsimonce at redhat.com>, "engine-devel" <engine-devel at ovirt.org>, "Eduardo Warszawski" <ewarszaw at redhat.com>, "Yeela
> Kaplan" <ykaplan at redhat.com>
> Sent: Tuesday, August 14, 2012 2:10:55 PM
> Subject: Re: [Engine-devel] Serial Execution of Async Tasks
> 
> Hi guys,
> 
> Thanks for all your comments!
> The correct response for many these points is to update the wiki.
> I'm enclosing here the quick-and-dirty replies just to keep this
> thread alive, and will update the wiki shortly.
> 
> See inline.
> 
> ----- Original Message -----
> > From: "Livnat Peer" <lpeer at redhat.com>
> > To: "Allon Mureinik" <amureini at redhat.com>
> > Cc: "Eli Mesika" <emesika at redhat.com>, "Liron Aravot"
> > <laravot at redhat.com>, "Federico Simoncelli"
> > <fsimonce at redhat.com>, "engine-devel" <engine-devel at ovirt.org>,
> > "Eduardo Warszawski" <ewarszaw at redhat.com>, "Yeela
> > Kaplan" <ykaplan at redhat.com>
> > Sent: Sunday, August 12, 2012 9:39:23 AM
> > Subject: Re: [Engine-devel] Serial Execution of Async Tasks
> > 
> > On 10/08/12 03:40, Eli Mesika wrote:
> > > 
> > > 
> > > ----- Original Message -----
> > >> From: "Allon Mureinik" <amureini at redhat.com>
> > >> To: "engine-devel" <engine-devel at ovirt.org>
> > >> Cc: "Eduardo Warszawski" <ewarszaw at redhat.com>, "Yeela Kaplan"
> > >> <ykaplan at redhat.com>, "Federico Simoncelli"
> > >> <fsimonce at redhat.com>, "Liron Aravot" <laravot at redhat.com>
> > >> Sent: Thursday, August 9, 2012 6:41:09 PM
> > >> Subject: [Engine-devel] Serial Execution of Async Tasks
> > >>
> > >> Hi guys,
> > >>
> > >> As you may know the engine currently has the ability to fire an
> > >> SPM
> > >> task, and be asynchronously be "woken-up" when it ends.
> > >> This is great, but we found the for the Live Storage Migration
> > >> feature we need something a bit complex - the ability to have a
> > >> series of async tasks in a single control flow.
> > >>
> > >> Here's my initial design for this, your comments and criticism
> > >> would
> > >> be welcome:
> > >> http://wiki.ovirt.org/wiki/Features/Serial_Execution_of_Asynchronous_Tasks_Detailed_Design
> > > 
> > > Apart from the short explanation & flow , since this is a
> > > detailed
> > > design , I would add
> > > 1) Class diagram
> > > 2) Flow diagram
> Good idea, I'll see if I can jimmy something up.
> 
> > > 
> > 
> > +1, it would help understanding the flow.
> > 
> > - It looks like you chose not re-use/extend the ExecutionHandler
> > (the
> > entity used for building the tasks view exposed to the users).
> > It might be a good idea to keep the separation between the engine
> > Jobs
> > and the underlying vdsm tasks, but I want to make sure you are
> > familiar
> > with this mechanism and ruled it out with a reason. If this is the
> > case
> > please share why you decided not to use it.
> As you said Jobs and Steps are pure engine entities - they can
> contain no VDSM tasks, one VDSM task, or plausibly, in the future,
> several tasks.
> Even /today/, AsyncTasks and Jobs/Steps are two different kinds of
> animals - I don't see any added value in mixing them together.
> 
> > 
> > 
> > - how does this design survives a jboss restart? Can you please a
> > section in the wiki to explain that.
> Basically, the way as a Command does today - the task is saved with
> the executionIndex, and continues when the command is woken up.
> I'll clarify this point in the wiki.
Added to the wiki.
> 
> > 
> > -successful execution -
> > * "CommandBase iterates over its SPMAsyncTaskHandlers" - when?
> This is the new suggested format of executeCommand(). I'll clarify
> this too.
Added to the wiki.

> > * If the second task is an HSM command (vs. SPM command), I think
> > you
> > should explain in the design how to handle such flows as well.
> HSM commands do not create AsyncTasks, as they do today - I will
> clarify this.
Added to the wiki.

> 
> > * Why do we need before task? can you give a concrete example of
> > what
> > would you do in such a method.
> Basically, /today/, command look like this:
> executeCommand() {
>   doStuffInTheDB();
>   runVdsCommand(someCommand);
> }
> 
> endSuccessfully() {
>   doMoreStuffInTheDB();
> }
> 
> endWithFailure() {
>   doMoreStuffForFailureInTheDB();
> }
> 
> In the new design, the entire doStuffInTheDB() should be moved to a
> breforeTask of the (only) SPMAsyncTaskHandler.
> 
> > 
> > - I see you added SPMAsyncTaskHandler, any reason not to use
> > SPMAsyncTasK to manage it own life-cycle?
> Conserving today's design - The SPMAsyncTaskHandler is the place to
> add additional, non-SPM, logic around the SPM task execution, like
> CommandBase allows today.
> 
> > 
> > - In the life-cycle managed by the SPMAsyncTaskHandler there is a
> > step
> > 'createTask - how to create the async task' can you please
> > elaborate
> > what are the options.
> new [any type of async task]
> > 
> > 
> > 
> > 
> > 
> > Livnat
> > 
> > >>
> > >>
> > >> -Allon
> > >> _______________________________________________
> > >> Engine-devel mailing list
> > >> Engine-devel at ovirt.org
> > >> http://lists.ovirt.org/mailman/listinfo/engine-devel
> > >>
> > > _______________________________________________
> > > Engine-devel mailing list
> > > Engine-devel at ovirt.org
> > > http://lists.ovirt.org/mailman/listinfo/engine-devel
> > > 
> > 
> > 
>