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From Dan Smith <dsm...@pivotal.io>
Subject Re: [DISCUSS] Controlling event dispatch to AsyncEventListener (review by Aug 22)
Date Fri, 16 Aug 2019 23:30:39 GMT
Hi Anil,

While I like the idea of matching the API of GatewaySender, I'm not sure I
see how this solves the problem. Is it required of the user to call pause
on the AsyncEventQueue as soon as it is created? How would someone do that
when creating AEQs with xml or cluster configuration? Maybe it would be
better to not dispatch any events until we are done creating all regions?

-Dan

On Fri, Aug 16, 2019 at 2:31 PM Anilkumar Gingade <agingade@pivotal.io>
wrote:

> Proposal to support controlling capability with event dispatch to
> AsyncEventQueue Listener.
>
> Wiki proposal page:
>
> https://cwiki.apache.org/confluence/display/GEODE/%5BDraft%5D+Controlling+event+dispatch+to+AsyncEventListener
>
> Here is the details from the wiki page:
> *Problem*
>
> *The Geode system requires AEQs to be configured before regions are
> created. If an AEQ listener is operating on a secondary region, this could
> cause listener to operate on a region which is not yet created or fully
> initialized (for region with co-located regions) which could result in
> missing events or dead-lock scenario between region (co-located region)
> creation threads. This scenario is likely to happen during persistence
> recovery; when AEQs are created in the start, the recovered AEQ events are
> dispatched immediately, thus invoking the AEQ listeners.*
> Anti-Goals
>
> None
> *Solution*
>
> *The proposed solution is to provide a way to control dispatching AEQ
> events to the AEQ Listeners, this could be done by adding "pause"  and
> "resume" capability to the AEQ, which will allow application to decide when
> to dispatch events to the listeners. *
>
>
> *The proposal is similar to existing "pause" and "resume" behavior on the
> GatewaySender, on which the AEQ is based on (AEQ implementation is a
> wrapper around GatewaySender). *
> Changes and Additions to Public Interfaces
>
> *The proposed APIs are:*
>
> *On "AsyncEventQueueFactory" interface - *
>
> *AsyncEventQueue pauseEventDispatchToListener();*
>
> *On "AsyncEventQueue" interface -*
>
> *boolean resumeEventDispatchToListener(); **returns true or false if the
> event dispatch is resumed successfully.*
>
>
> *The constraints on the pauseEventDispatchToListener() will remain similar
> to as in "GatewaySender.pause()" :*
>
> "It should be kept in mind that the events will still be getting queued
> into the queue. The scope of this operation is the VM on which it is
> invoked. In case the AEQ is parallel, the AEQ will be paused on individual
> node where this API is called and the AEQ on other VM's can still dispatch
> events. In case the AEQ is not parallel, and the running AEQ on which this
> API is invoked is not primary then primary AEQ will still continue
> dispatching events."
> Performance Impact
>
>
> *This will have similar performance and resource implication as with the
> "GatewaySender.pause()" functionality. If the AEQ is not resumed or kept in
> "pause" state for long, it may start consuming the configured memory and
> overflow it into disk and may cause disk full scenario.*
> Backwards Compatibility and Upgrade Path
>
> *Impact with rolling upgrade: *
>
> *As the api is applicable at individual VM level, there is no message
> serialization changes involved. And only applicable to the events getting
> dispatched to the listeners on that VM. And the AEQ which are replicated
> (for redundancy) continues to work as before.*
>
> *Backward compatibility requirements: *
>
> *None. The AEQs are configured and managed at the server side. There is no
> messaging involved between client/server.*
>
> *Disk formatting changes:*
>
> *None.*
>
> *Deprecation and Application Changes:*
>
>
> *None. If needed, the existing application can be modified to control event
> dispatch with AEQ listener.*
> Prior Art
>
> *Without this, the AEQ listeners operating on other regions could
> experience missing events or dead lock, if there are co-located regions.*
>
> *This approach is simple and can take advantage of the existing
> functionality that is already supported in GatewaySender on which AEQ is
> based on.*
>

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