Getting on the same page with @Clustered @Singleton

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Getting on the same page with @Clustered @Singleton

Radoslav Husar
Hi guys,

I just want to sync up with everyone what's the plan on EE6's @Singleton
running on multiple JVMs in 7.1*.

There is a common misconception that @Singleton is acting at cluster
level. This is nay. The EE spec says:

A Singleton session bean is a session bean component that is
instantiated once per application. In cases where the container is
distributed over many virtual machines, each application will have one
bean instance of the Singleton *for each JVM*.


However the concept of @Clustered @Singleton where there is only 1
failure-resistant bean instance within the cluster replicating state
does make a lot of sense. Having to sync on the persistence level sounds
dreadful. In one sense it is the successor of AS 5's singleton-ha which
was deployment-level mechanism.

Is is possible to have this even though it is kind of violating the EE spec?


David is requesting to fail the deployment of such:
https://issues.jboss.org/browse/AS7-2887

Does it mean that we wont have it in 7.1? Maybe later?


Cheers,
Rado


* EAP 6.0
--
Radoslav Husar

JBoss QE
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Re: Getting on the same page with @Clustered @Singleton

Andrig Miller
The other complication, is that you may have a Singleton that has no state to replicate.  In that case, the single instance, with no replication makes sense.

Andy

----- Original Message -----

> From: "Radoslav Husar" <[hidden email]>
> To: [hidden email], "David Lloyd" <[hidden email]>, "Paul Ferraro" <[hidden email]>
> Sent: Wednesday, December 7, 2011 10:50:35 AM
> Subject: [jboss-as7-dev] Getting on the same page with @Clustered @Singleton
>
> Hi guys,
>
> I just want to sync up with everyone what's the plan on EE6's
> @Singleton
> running on multiple JVMs in 7.1*.
>
> There is a common misconception that @Singleton is acting at cluster
> level. This is nay. The EE spec says:
>
> A Singleton session bean is a session bean component that is
> instantiated once per application. In cases where the container is
> distributed over many virtual machines, each application will have
> one
> bean instance of the Singleton *for each JVM*.
>
>
> However the concept of @Clustered @Singleton where there is only 1
> failure-resistant bean instance within the cluster replicating state
> does make a lot of sense. Having to sync on the persistence level
> sounds
> dreadful. In one sense it is the successor of AS 5's singleton-ha
> which
> was deployment-level mechanism.
>
> Is is possible to have this even though it is kind of violating the
> EE spec?
>
>
> David is requesting to fail the deployment of such:
> https://issues.jboss.org/browse/AS7-2887
>
> Does it mean that we wont have it in 7.1? Maybe later?
>
>
> Cheers,
> Rado
>
>
> * EAP 6.0
> --
> Radoslav Husar
>
> JBoss QE
> _______________________________________________
> jboss-as7-dev mailing list
> [hidden email]
> https://lists.jboss.org/mailman/listinfo/jboss-as7-dev
>
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Re: Getting on the same page with @Clustered @Singleton

David Lloyd
Here's a brief summary of what we've decided so far on this.  We've
determined that a @Clustered @Singleton would, if implemented, act
similarly to a @Clustered @Stateful which only has one session.

When it comes down to spec, any kind of clustering is really non-spec
behavior.  Having such features doesn't mean we aren't spec-conformant,
it just means we have additional functionality which goes beyond
specification.

Since we don't have @Clustered @Singleton today, this isn't considered a
high priority for the next release.  But I suspect we could deliver this
for 7.2 if we wanted to.

On 12/07/2011 12:15 PM, Andrig Miller wrote:

> The other complication, is that you may have a Singleton that has no state to replicate.  In that case, the single instance, with no replication makes sense.
>
> Andy
>
> ----- Original Message -----
>> From: "Radoslav Husar"<[hidden email]>
>> To: [hidden email], "David Lloyd"<[hidden email]>, "Paul Ferraro"<[hidden email]>
>> Sent: Wednesday, December 7, 2011 10:50:35 AM
>> Subject: [jboss-as7-dev] Getting on the same page with @Clustered @Singleton
>>
>> Hi guys,
>>
>> I just want to sync up with everyone what's the plan on EE6's
>> @Singleton
>> running on multiple JVMs in 7.1*.
>>
>> There is a common misconception that @Singleton is acting at cluster
>> level. This is nay. The EE spec says:
>>
>> A Singleton session bean is a session bean component that is
>> instantiated once per application. In cases where the container is
>> distributed over many virtual machines, each application will have
>> one
>> bean instance of the Singleton *for each JVM*.
>>
>>
>> However the concept of @Clustered @Singleton where there is only 1
>> failure-resistant bean instance within the cluster replicating state
>> does make a lot of sense. Having to sync on the persistence level
>> sounds
>> dreadful. In one sense it is the successor of AS 5's singleton-ha
>> which
>> was deployment-level mechanism.
>>
>> Is is possible to have this even though it is kind of violating the
>> EE spec?
>>
>>
>> David is requesting to fail the deployment of such:
>> https://issues.jboss.org/browse/AS7-2887
>>
>> Does it mean that we wont have it in 7.1? Maybe later?
>>
>>
>> Cheers,
>> Rado
>>
>>
>> * EAP 6.0
>> --
>> Radoslav Husar
>>
>> JBoss QE
>> _______________________________________________
>> jboss-as7-dev mailing list
>> [hidden email]
>> https://lists.jboss.org/mailman/listinfo/jboss-as7-dev
>>


--
- DML
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Re: Getting on the same page with @Clustered @Singleton

Jason T. Greene
Note that singletons can express and rely on start order, which makes clustering them bend the spec rules (failover can either violate that expectation or it can require graph coupled failover) That's part of the reason it's deferred. It requires a bit more thought.

Sent from my iPhone

On Dec 7, 2011, at 1:11 PM, "David M. Lloyd" <[hidden email]> wrote:

> Here's a brief summary of what we've decided so far on this.  We've
> determined that a @Clustered @Singleton would, if implemented, act
> similarly to a @Clustered @Stateful which only has one session.
>
> When it comes down to spec, any kind of clustering is really non-spec
> behavior.  Having such features doesn't mean we aren't spec-conformant,
> it just means we have additional functionality which goes beyond
> specification.
>
> Since we don't have @Clustered @Singleton today, this isn't considered a
> high priority for the next release.  But I suspect we could deliver this
> for 7.2 if we wanted to.
>
> On 12/07/2011 12:15 PM, Andrig Miller wrote:
>> The other complication, is that you may have a Singleton that has no state to replicate.  In that case, the single instance, with no replication makes sense.
>>
>> Andy
>>
>> ----- Original Message -----
>>> From: "Radoslav Husar"<[hidden email]>
>>> To: [hidden email], "David Lloyd"<[hidden email]>, "Paul Ferraro"<[hidden email]>
>>> Sent: Wednesday, December 7, 2011 10:50:35 AM
>>> Subject: [jboss-as7-dev] Getting on the same page with @Clustered @Singleton
>>>
>>> Hi guys,
>>>
>>> I just want to sync up with everyone what's the plan on EE6's
>>> @Singleton
>>> running on multiple JVMs in 7.1*.
>>>
>>> There is a common misconception that @Singleton is acting at cluster
>>> level. This is nay. The EE spec says:
>>>
>>> A Singleton session bean is a session bean component that is
>>> instantiated once per application. In cases where the container is
>>> distributed over many virtual machines, each application will have
>>> one
>>> bean instance of the Singleton *for each JVM*.
>>>
>>>
>>> However the concept of @Clustered @Singleton where there is only 1
>>> failure-resistant bean instance within the cluster replicating state
>>> does make a lot of sense. Having to sync on the persistence level
>>> sounds
>>> dreadful. In one sense it is the successor of AS 5's singleton-ha
>>> which
>>> was deployment-level mechanism.
>>>
>>> Is is possible to have this even though it is kind of violating the
>>> EE spec?
>>>
>>>
>>> David is requesting to fail the deployment of such:
>>> https://issues.jboss.org/browse/AS7-2887
>>>
>>> Does it mean that we wont have it in 7.1? Maybe later?
>>>
>>>
>>> Cheers,
>>> Rado
>>>
>>>
>>> * EAP 6.0
>>> --
>>> Radoslav Husar
>>>
>>> JBoss QE
>>> _______________________________________________
>>> jboss-as7-dev mailing list
>>> [hidden email]
>>> https://lists.jboss.org/mailman/listinfo/jboss-as7-dev
>>>
>
>
> --
> - DML
> _______________________________________________
> jboss-as7-dev mailing list
> [hidden email]
> https://lists.jboss.org/mailman/listinfo/jboss-as7-dev

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Re: Getting on the same page with @Clustered @Singleton

Paul Ferraro
In reply to this post by Radoslav Husar
Rado,

We've decided to defer on supporting @Clustered @Singleton in 7.1.

As we also discussed, HA-singleton will still be supported in 7.1,
though it will only operate on MSC services.

Paul

On Wed, 2011-12-07 at 18:50 +0100, Radoslav Husar wrote:

> Hi guys,
>
> I just want to sync up with everyone what's the plan on EE6's @Singleton
> running on multiple JVMs in 7.1*.
>
> There is a common misconception that @Singleton is acting at cluster
> level. This is nay. The EE spec says:
>
> A Singleton session bean is a session bean component that is
> instantiated once per application. In cases where the container is
> distributed over many virtual machines, each application will have one
> bean instance of the Singleton *for each JVM*.
>
>
> However the concept of @Clustered @Singleton where there is only 1
> failure-resistant bean instance within the cluster replicating state
> does make a lot of sense. Having to sync on the persistence level sounds
> dreadful. In one sense it is the successor of AS 5's singleton-ha which
> was deployment-level mechanism.
>
> Is is possible to have this even though it is kind of violating the EE spec?
>
>
> David is requesting to fail the deployment of such:
> https://issues.jboss.org/browse/AS7-2887
>
> Does it mean that we wont have it in 7.1? Maybe later?
>
>
> Cheers,
> Rado
>
>
> * EAP 6.0


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