[infinispan-dev] About size()

Mircea Markus mmarkus at redhat.com
Wed Oct 8 10:11:55 EDT 2014


On Oct 6, 2014, at 12:44, Tristan Tarrant <ttarrant at redhat.com> wrote:

> I think we should provide correct implementations of size() (and others) 
> and provide shortcut implementations using our usual Flag API (e.g. 
> SKIP_REMOTE_LOOKUP).

for keySet and values, Will's distributed iteration is a way nicer way of doing it, as it only fetches the data iteratively. Better to throw an exception and point user to the distributed iterator.

> 
> Tristan
> 
> On 06/10/14 12:57, Sanne Grinovero wrote:
>> On 3 October 2014 18:38, Dennis Reed <dereed at redhat.com> wrote:
>>> Since size() is defined by the ConcurrentMap interface, it already has a
>>> precisely defined meaning.  The only "correct" implementation is E.
>> +1
>> 
>>> The current non-correct implementation was just because it's expensive
>>> to calculate correctly.  I'm not sure the current impl is really that
>>> useful for anything.
>> +1
>> 
>> And not just size() but many others from ConcurrentMap.
>> The question is if we should drop the interface and all the methods
>> which aren't efficiently implementable, or fix all those methods.
>> 
>> In the past I loved that I could inject "Infinispan superpowers" into
>> an application making extensive use of Map and ConcurrentMap without
>> changes, but that has been deceiving and required great care such as
>> verifying that these features would not be used anywhere in the code.
>> I ended up wrapping the Cache implementation in a custom adapter which
>> would also implement ConcurrentMap but would throw a RuntimeException
>> if any of the "unallowed" methods was called, at least I would detect
>> violations safely.
>> 
>> I still think that for the time being - until a better solution is
>> planned - we should throw exceptions.. alas that's an old conversation
>> and it was never done.
>> 
>> Sanne
>> 
>> 
>>> -Dennis
>>> 
>>> On 10/03/2014 03:30 AM, Radim Vansa wrote:
>>>> Hi,
>>>> 
>>>> recently we had a discussion about what size() returns, but I've
>>>> realized there are more things that users would like to know. My
>>>> question is whether you think that they would really appreciate it, or
>>>> whether it's just my QA point of view where I sometimes compute the
>>>> 'checksums' of cache to see if I didn't lost anything.
>>>> 
>>>> There are those sizes:
>>>> A) number of owned entries
>>>> B) number of entries stored locally in memory
>>>> C) number of entries stored in each local cache store
>>>> D) number of entries stored in each shared cache store
>>>> E) total number of entries in cache
>>>> 
>>>> So far, we can get
>>>> B via withFlags(SKIP_CACHE_LOAD).size()
>>>> (passivation ? B : 0) + firstNonZero(C, D) via size()
>>>> E via distributed iterators / MR
>>>> A via data container iteration + distribution manager query, but only
>>>> without cache store
>>>> C or D through
>>>> getComponentRegistry().getLocalComponent(PersistenceManager.class).getStores()
>>>> 
>>>> I think that it would go along with users' expectations if size()
>>>> returned E and for the rest we should have special methods on
>>>> AdvancedCache. That would of course change the meaning of size(), but
>>>> I'd say that finally to something that has firm meaning.
>>>> 
>>>> WDYT?
>>>> 
>>>> Radim
>>>> 
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>> 
> 
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Cheers,
-- 
Mircea Markus
Infinispan lead (www.infinispan.org)







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