[infinispan-dev] replacing the (FineGrained)AtomicMap with grouping

[Randall Hauch]

IMO, the primary benefit of the FGAM is that you can aggregate your entries into a single entry that is a real aggregate: read the map and you get all the FGAM's entries in one fell swoop. IIUC, your proposal loses this capability for a single read of all aggregate parts. Is that right?

On Sep 20, 2013, at 11:49 AM, Mircea Markus <mmarkus at redhat.com> wrote:

> Hi,
> 
> Most of the FGAM functionality can be achieved with grouping, by using the FGAM key as a grouping key.
> The single bit that seems to be missing from grouping to equivalent the functionality of FGAM is obtaining all the entries under a single group. IOW a method like:
> 
> Map<K,V> groupedKeys = Cache.getGroup(groupingKey, KeyFilter);
> 
> This can be relatively easily implemented with the same performance as an AtomicMap lookup.
> 
> Some other differences worth mentioning:
> - the cache would contain more entries in the grouping API approach. Not sure if this is really a problem though.
> - in order to assure REPEATABLE_READ, the AM (including values) is brought on the node that reads it (does't apply to FGAM). Not nice.
> - people won't be able to lock an entire group (the equivalent of locking a AM key). I don't think this is a critical requirement, and also can be worked around. Or added as a built in function if needed.
> 
> I find the idea of dropping FGAM and only using grouping very tempting:
> - there is logic duplication between Grouping and (FG)AM (the locality, fine grained locking) that would be removed
> - FGAM and AM semantic is a bit ambiguous in corner cases
> - having a Cache.getGroup does make sense in a general case
> - reduce the code base
> 
> What do people think? 
> 
> Cheers,
> -- 
> Mircea Markus
> Infinispan lead (www.infinispan.org)
> 
> 
> 
> 
> 
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