Re: [Engine-devel] Serial Execution of Async Tasks

22 Aug 2012


      ----- Original Message -----
...
From: "Allon Mureinik" <amureini@redhat.com>
To: "Livnat Peer" <lpeer@redhat.com>
Cc: "Eli Mesika" <emesika@redhat.com>, "Liron Aravot" <laravot@redhat.com>, "Federico Simoncelli"
<fsimonce@redhat.com>, "engine-devel" <engine-devel@ovirt.org>, "Eduardo Warszawski" <ewarszaw@redhat.com>, "Yeela
Kaplan" <ykaplan@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@redhat.com>
To: "Allon Mureinik" <amureini@redhat.com>
Cc: "Eli Mesika" <emesika@redhat.com>, "Liron Aravot"
<laravot@redhat.com>, "Federico Simoncelli"
<fsimonce@redhat.com>, "engine-devel" <engine-devel@ovirt.org>,
"Eduardo Warszawski" <ewarszaw@redhat.com>, "Yeela
Kaplan" <ykaplan@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@redhat.com>
To: "engine-devel" <engine-devel@ovirt.org>
Cc: "Eduardo Warszawski" <ewarszaw@redhat.com>, "Yeela Kaplan"
<ykaplan@redhat.com>, "Federico Simoncelli"
<fsimonce@redhat.com>, "Liron Aravot" <laravot@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_D...
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
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