[infinispan-dev] Optional in listener events

[Adrian Nistor]

No. CQ absolutely needs the previous value.


On 08/24/2016 12:54 PM, Pedro Ruivo wrote:
> If we can drop the pre-events, it would be possible to skip the
> loading/wrapping of the previous value. The method DataContainer.put()
> could return the previous value/metadata that could be used to trigger
> the post-event.
>
> However, it has a problem that I haven't solved it yet: if the value is
> not in memory it will not be loaded (cache-stores / rebalance in progress).
>
> Would it work for CQ?
>
> Cheers,
> Pedro
>
> On 22-08-2016 19:15, William Burns wrote:
>> I like the idea of having a variable to set on the listener annotation.
>> This way we can know for sure if we need to force previous values for
>> some listeners and not for others.
>>
>> It seems the default should be to force the previous value to be more
>> inline with the current behavior, but I fear no one will use the
>> opposite in this case though.  What do you guys think?
>>
>> On Mon, Aug 22, 2016 at 4:31 AM Adrian Nistor <anistor at redhat.com
>> <mailto:anistor at redhat.com>> wrote:
>>
>>      Hi Radim,
>>
>>      Continuous query is built on top of these listeners. CQ _always_ needs
>>      the previous value and it is very convenient in this case that the
>>      command is forced to load the previous value. I imagine there may be
>>      other use cases where we cannot live without the prev value.
>>
>>      I think the listener should be able to state if it needs the prev value
>>      at registration time. Maybe add a new attribute in the Listener
>>      annotation? Similar to how we handled Observation.
>>
>>      Adrian
>>
>>      On 08/19/2016 11:34 PM, Radim Vansa wrote:
>>      > Hi,
>>      >
>>      > as I am trying to simplify current entry wrapping and distribution
>>      code,
>>      > I often find that listeners can get wrong previous value in the event,
>>      > and it sometimes forces the command to load the value even if it
>>      is not
>>      > needed for the command.
>>      >
>>      > I am wondering if we should change the previous value in events to
>>      > Optional - we can usually at least detect that we cannot provide a
>>      > reliable value (e.g. after retry due to topology change, or
>>      because the
>>      > command did not bothered to load the previous value from cache loader)
>>      > and return empty Optional.
>>      >
>>      > WDYT?
>>      >
>>      > Radim
>>      >
>>
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>>
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