1:31 p.m.
Hey,
There is an interesting request from community to include an Address along with a Future
returned for a subtask being executed [1].
I think it makes sense what this user wants. We might create Future sub interface that has
getAddress method and we can return an object implementing that interface instead of plain
Future. In some new major release we can officially change the signature of these
DistributedExecutorService methods to return i.e TargetedFuture - it would not break
existing clients. Maybe even make TargetedFuture extend NotifyingFuture.
Any thoughts?
Vladimir
[1] https://community.jboss.org/thread/237442
3:25 p.m.
I'm a bit skeptical.
It might sound a sensible request currently, but if you do so you
inherently "promise" that tasks are going to be executed on a specific
server; AFAIK we promise execution on data locality, but maintaining a
good level of flexibility you can evolve your system to smarter load
balancing of tasks, failover operations, etc..
If you expose execution details, you won't be able to develop any of
that in future.
To make an example from the database world - seems the analogy is
common these days - it's like you run a SELECT statement but want to
pick which CPU core is going to be used. That would be really odd, as
you would take away the option from the scheduler to make an effective
choice.
Still, this approach might be desirable for a database which doesn't
do any smart scheduling.
Some of these concerns might be mitigated if you return the Address of
where the task *was* executed, after it's done. I still don't think it
should be of user's interest but at least you would be able to
implement rescheduling or failover policies in future.
Sanne
On 26 February 2014 19:31, Vladimir Blagojevic <vblagoje(a)redhat.com> wrote:
10:58 a.m.
On Feb 27, 2014, at 3:28 PM, Vladimir Blagojevic <vblagoje(a)redhat.com> wrote:
We allow execution to be bound on a specific address: http://goo.gl/H5qTJZ
I see your point with data locality vs. specific server.
We already have failure policies in place, but the user only needs to audit the failure,
not to failover. If users are interested on knowing the failures, another way of doing it
is the current future, in the Future.get to throw a custom exception (subclass of
ExecutionException) containing as information where the execution failed.
Cheers,
--
Mircea Markus
Infinispan lead (www.infinispan.org)
12:13 p.m.
On 27 February 2014 16:58, Mircea Markus <mmarkus(a)redhat.com> wrote:
I know but I think that smells :)
Stuff like _Address_ should be an implementation detail. Maybe one day
you'll see why and we'll deprecate it ;-)
Right, but the question is if the user really wants to know the
intermediate failures? I suspect that if someone asks for this, he's
actually wishing to implement his own failower policy & monitoring.
From the point of view of someone running a database query, I think
the user would love to ignore issues altogether, but the real world
forces him to at least consider that the whole operation might fail.
Sending him specific notifications or exceptions of something that was
succesfull but was actually run on a different resource set than what
was originally planned is I'd say an exotic request.
I like the idea of providing additional information in a Future
subtype, but I don't think you should throw it on a get() operation.
You could simply add getters to the FutureExtended to retrieve like an
execution plan history, a trace of intermediate failures, etc.
Sanne
12:40 p.m.
On Thu, Feb 27, 2014 at 8:13 PM, Sanne Grinovero <sanne(a)infinispan.org>wrote:
I don't think the user was after the address of the "real" executing node,
I believe he just wanted a way to map each Future to the target address
doing a submitEverywhere(task).
That sounds good, but we shouldn't limit that to just the result of one
distributed task execution. We could take the opportunity to return
something other than List<Future> from submitEverywhere(task) as well,
doing a foreach to get all the results is a bit tedious. And even if we'd
like users to treat the results from different nodes as interchangeable,
sometimes they're not, so a way of getting the result from one particular
node would also be useful.
4050
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6 comments
4 participants
participants (4)
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Dan Berindei -
Mircea Markus -
Sanne Grinovero -
Vladimir Blagojevic