[infinispan-dev] New Cache Entry Notifications

[Sanne Grinovero]

On 23 January 2014 17:54, Mircea Markus <mmarkus at redhat.com> wrote:
>
> On Jan 23, 2014, at 5:48 PM, William Burns <mudokonman at gmail.com> wrote:
>
>> Hello all,
>>
>> I have been working with notifications and most recently I have come
>> to look into events generated when a new entry is created.  Now
>> normally I would just expect a CacheEntryCreatedEvent to be raised.
>> However we currently raise a CacheEntryModifiedEvent event and then a
>> CacheEntryCreatedEvent.  I notice that there are comments around the
>> code saying that tests require both to be fired.
>
> it doesn't sound right to me: modified is different than created.

I'd tend to agree with you, still it's a matter of perception as I could say
"a key is changing value from null to some new value so it's an update"..
I realize it's a bit far fetched, still if you start introducing
tombstones for eventual consistency you can have a longer history of
changes to append to even if it's just a "creation".

For example with this sequence of commands:

Put(K1, V1), Remove(K1), Put(K1, V2) < Creation event?

As the history sequence for this entry is
V1 - null - V2

And in case of asynchronous CacheStores, Remote eventlistener, X-site,
.. and all other features where you might have coalescing of changes
applied, this sequence could be "compacted" as

V1 - V2

Is the write of V2 still a creation event?

I don't necessarily disagree with the choice, but it's not that simple
and will have consequent complexities down the road.

Personally I think you should drop the differentiation between the two
event types, as it's over-promising on something that we can't deliver
consistently.

Sanne

>
>>
>> I am wondering if anyone has an objection to only raising a
>> CacheEntryCreatedEvent on a new cache entry being created.  Does
>> anyone know why we raise both currently?  Was it just so the
>> PutKeyValueCommand could more ignorantly just raise the
>> CacheEntryModified pre Event?
>>
>> Any input would be appreciated, Thanks.
>
> Cheers,
> --
> Mircea Markus
> Infinispan lead (www.infinispan.org)
>
>
>
>
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