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From Denis Magda <dma...@gridgain.com>
Subject Re: Missing ways to get access to Ignite CacheEntry
Date Fri, 18 Dec 2015 10:44:16 GMT
Hi Andrey,

I got you, thanks for the clarification.

So since you're storing a computed value in some local data structure 
what is stored in the Ignite cache as a value in such a case? There 
should be something.
Why don't you (or can't you) store a version identifier in that value 
that is located in the Ignite cache? This should work perfectly well for 
you use-case.

Personally I'm against adding CacheEntry to a response of every get like 
operation that happens over a cache (get, getAll, SQL & Scan queries).
This will add extra size to every response and only in rare cases 
someone will benefit from it.
However, what if we add a special configuration parameter to 
CacheConfiguration that will manage whether CacheEntry has to be passed 
as a part of a response or not? Igniters, what do you think on this?


Regards,
Denis


On 12/17/2015 9:09 AM, Andrey Kornev wrote:
> Denis,In this case I used the term "caching" in general sense, meaning saving the computed
value for later. I didn't mean the Ignite cache.Sorry about the confusion.Andrey
>      _____________________________
> From: Denis Magda <dmagda@gridgain.com>
> Sent: Wednesday, December 16, 2015 9:48 PM
> Subject: Re: Missing ways to get access to Ignite CacheEntry
> To:  <dev@ignite.apache.org>
>
>
>                     Hi Romain,
>      
>   I'm a bit confused cause initially you saying that
>      
>   /The value is computed on first access and it is then cached
>      
>   /and then you add that
>      
>   /One constraint is that the computed value is not serializable. //
>   /
>      
>      
>   Ignite won't be able to store a value of cache if serialization is not
>   supported for it by some reason.
>      
>   Please clarify here. Probably I'm missing something from your description.
>      
>   --
>   Denis
>      
>   On 12/16/2015 6:21 PM, Andrey Kornev wrote:
>   > Romain
>   >
>   > I suggest you be very careful using the invoke() functionality. As explained in
this posting (and the follow-ups)
>   >    http://mail-archives.apache.org/mod_mbox/ignite-dev/201511.mbox/%3CSNT147-W14D2736E1374450B685721CF000%40phx.gbl%3E
>   > the correct usage of the invoke() may be difficult, to put it politely.
>   >
>   > @Denis Very briefly, the use case is "conditional re-compute". There is a pretty
expensive computation that needs to be applied to each entry on demand. The value is computed
on first access and it is then cached along with the current version of the cache entry. 
The  value must be recomputed on next access only if the entry has been modified.
>   >
>   > If anyone has a better idea how to achieve something like that, please do share!
One constraint is that the computed value is not  serializable.
>   >
>   > Cheers
>   > Andrey
>   >
>   >> Subject: Re: Missing ways to get access to Ignite CacheEntry
>   >> To: dev@ignite.apache.org
>   >> From: dmagda@gridgain.com
>   >> Date: Wed, 16 Dec 2015 16:11:48 +0300
>   >>
>   >> Romain,
>   >>
>   >> If it's implemented this way for now it doesn't mean that we can't
>   >> enhance the API for other use cases ;)
>   >> As I said presently it's supported for limited number of methods mostly
>   >> by performance reasons.
>   >>
>   >> Please go ahead and try invoke/invokeAll and if it doesn't work fine for
>   >> you we can keep discussing what to do next.
>   >>
>   >> Regards,
>   >> Denis
>   >>
>   >> On 12/16/2015 1:53 PM, Romain Gilles wrote:
>   >>> Hi Denis,
>   >>> Thanks for you replay. And sorry to not double check it before. I see
that
>   >>> if I want to work with CacheEntry, I need to use the invoke method in
order
>   >>> to return the CacheEntry. This is the way I should do it. It sounds like
>   >>> complicated for "just" getting an entry. But if you say this is the way
I
>   >>> will do it like that. I was just think that it could be a common use case
>   >>> and therefore provide it as a shortcut.
>   >>>
>   >>> Thanks,
>   >>>
>   >>> Romain.
>   >>>
>   >>> Le mer. 16 déc. 2015 à 11:34, Denis Magda <dmagda@gridgain.com>
a écrit :
>   >>>
>   >>>> Hi Romain,
>   >>>>
>   >>>> As the current documentation of org.apache.ignite.cache.CacheEntry
>   >>>> states it's possible to get a reference to CacheEntry and its version
>   >>>> only for methods that are executed over local data set stored on a
node.
>   >>>> Among such methods are invoke & invokeAll and randomEntry.
>   >>>>
>   >>>> You probably can get a CacheEntry and its non null version when a
cache
>   >>>> iterator is in use but the version will be 'null', as far as I remember,
>   >>>> for those entries that are loaded from remote nodes.
>   >>>> Presently Ignite doesn't transfer the version from remote nodes as
a
>   >>>> part of response by perform reasons.
>   >>>>
>   >>>> Please elaborate more on your particular use case and what API you
would
>   >>>> like to add in order to support it.
>   >>>>
>   >>>> --
>   >>>> Denis
>   >>>>
>   >>>> On 12/16/2015 12:58 PM, Romain Gilles wrote:
>   >>>>> Hi Igniters,
>   >>>>> I'm looking for a way to get access to the Ignite CacheEntry.
For now
>   >>>> this
>   >>>>> is the ways I found:
>   >>>>>
>   >>>>>       - Through the queris
>   >>>>>       - Through jsr 107 Cache Iterable
>   >>>>>       - Through jsr 107 Cache itterator
>   >>>>>       - Through IgniteCache::randomEntry()
>   >>>>>
>   >>>>> If I remember correctly it was possible to get the CacheEntry
from a
>   >>>> given
>   >>>>> key in old version of gridgain community
>   >>>>> version: GridCacheProjection::entry(K key) GridCacheEntry<K,V>
>   >>>>> I think it could be a good to introduce this feature at IgniteCache
>   >>>> level.
>   >>>>> Or maybe there is an other way to do it.
>   >>>>>
>   >>>>> Thanks,
>   >>>>>
>   >>>>> Romain.
>   >>>>>
>   >
>      
>         
>
>
>    


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