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From Denis Mekhanikov <dmekhani...@gmail.com>
Subject Re: Continuous query deployment
Date Mon, 22 Oct 2018 08:46:10 GMT
Ilya,

Disabling P2P class loading for CQ with *autoUnsubscribe=false* is a
minimum, that should be done.
But it will only solves one of the existing problems.
It's still unclear, how to undeploy such queries.
Continuous queries with *autoUnsubscribe=true* have different semantic with
the ones with *autoUnsubscribe=false*.

The first of them is designed to deliver cache events to the subscriber.
They can't exist without the subscriber node, so they are automatically
undeployed, when the subscriber leaves.
I don't see any problems in using  P2P class loading for them.

The second one is needed to deploy a set of listeners, that are collocated
to data.
In this case the subscriber is not needed, so we don't undeploy the query,
when the subscriber leaves.
But we still have a dependency on the subscriber, since only him can
undeploy the query or redeploy it with different parameters.
Such queries should have a name or Id, that other nodes will use to get a
handle of them.
And P2P class loading is not applicable here, since the query may outlive
the initiator.

Val,

We didn't start working on service hot redeployment yet.
We tentatively agreed, that Deployment SPI it a good candidate as a tool
for this task.

Denis

чт, 18 окт. 2018 г. в 18:44, Valentin Kulichenko <
valentin.kulichenko@gmail.com>:

> Denis,
>
> I agree that p2p loading is not the best choice for CQs. Do you know if
> we've already done anything in that area for the Service Grid? Are we
> using/going to use Deployment SPI there as well? Either way, I think it
> would make sense if services and CQs should end up using the same mechanism
> for dynamic loading.
>
> -Val
>
> On Thu, Oct 18, 2018 at 8:36 AM Ilya Kasnacheev <ilya.kasnacheev@gmail.com
> >
> wrote:
>
> > Hello!
> >
> > Is it possible to simply disable P2P class loading for remote filter of
> > continuous queries with autoUnsubscribe = true?
> >
> > Regards,
> > --
> > Ilya Kasnacheev
> >
> >
> > чт, 18 окт. 2018 г. в 18:31, Denis Mekhanikov <dmekhanikov@gmail.com>:
> >
> > > Igniters,
> > >
> > > I'm concerned with our continuous query API and deployment procedure.
> > >
> > > Continuous queries have remote filters, that can be deployed over peer
> > > class loading mechanism (this functionality is currently broken though:
> > > IGNITE-3653 <https://issues.apache.org/jira/browse/IGNITE-3653>,
> > > IGNITE-9181
> > > <https://issues.apache.org/jira/browse/IGNITE-9181>).
> > > In usual cases P2P class loading makes sense, but problems begin when a
> > > node, that deployed the CQ, leaves cluster. By default the CQ is
> > undeployed
> > > in this case. But ContinuousQuery has *autoUnsubscribe*
> > > <
> > >
> >
> https://ignite.apache.org/releases/latest/javadoc/org/apache/ignite/cache/query/ContinuousQuery.html#setAutoUnsubscribe-boolean-
> > > >
> > > property. If set to true, it lets a continuous query stay in cluster,
> > when
> > > initiator leaves.
> > > So, you may end up in a situation, when a continuous query remote
> filter
> > is
> > > deployed in a cluster, but the node, that the class was loaded from, is
> > > already gone.
> > > New nodes won't have where to load the remote filter class from in this
> > > case. Also existing nodes may have problems, since class loading of
> > > dependencies of the loaded class happens lazily (and cannot happen
> > > eagerly), so they also need the initiator node.
> > >
> > > The *autoUnsubscribe* property helps to deploy continuous queries, that
> > > listen to cache updates and react to them in the remote filters. This
> is
> > > pretty convenient, since it allows cache updates be processed locally,
> > > right where updates happen, without sending data over network. Such
> > > continuous query may not even have a local listener, so initiator node
> > may
> > > deploy the query and leave.
> > >
> > > *BUT*
> > >
> > >    - The deployed CQ becomes impossible to undeploy. It stays in the
> > >    cluster till the end of times.
> > >    - This case looks like a miss-use of the remote filters. They should
> > >    *filter*, but not *listen* and *react*. Remote filter should be a
> > >    stateless predicate rather than a clever callback.
> > >    - It causes the problems with P2P class loading, mentioned above.
> > >
> > > So, I'd like to see the *autoUnsubscribe *property deprecated and
> > removed.
> > >
> > > This use-case should be covered by a different mechanism, that will
> allow
> > > to deploy a listener into a cluster by name. It should support
> deployment
> > > SPI <https://apacheignite.readme.io/docs/deployment-spi> instead of
> peer
> > > class loading. It may be built on top of continuous queries, but have a
> > > more suitable API.
> > >
> > > What do you think?
> > >
> > > Denis
> > >
> >
>

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