[Engine-devel] Serial Execution of Async Tasks

[Allon Mureinik]

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.

> 
> -successful execution -
> * "CommandBase iterates over its SPMAsyncTaskHandlers" - when?
This is the new suggested format of executeCommand(). I'll clarify this too.

> * 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.

> * 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
> > 
> 
>