[infinispan-dev] New Cache Entry Notifications

[Mircea Markus]

On Jan 27, 2014, at 9:35 AM, Sanne Grinovero <sanne at infinispan.org> wrote:

> 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,

there were actually discussions about implementing all the ISPN operations as a single generic one, so you do have a point :-)

> 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".

Whilst I agree with you in theory, IMO the users have a clear expectations on what an update vs an create is (as in CRUD). Using tombstones is an implementation detail, but there is a general accepted semantical difference between a create and an update. 

> 
> 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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Cheers,
-- 
Mircea Markus
Infinispan lead (www.infinispan.org)