Exactly, in a monitoring application you wouldn't need the exact number of key-value mappings in the cache.
The number of entries in memory and/or on disk should be much more interesting, and we wouldn't have to worry about duplicated/missing/expired entries to show that. On Fri, Oct 10, 2014 at 5:06 PM, Tristan Tarrant <ttarr...@redhat.com> wrote: > What's wrong with sum(Datacontainer.size())/numOwners ? > > Tristan > > On 10/10/14 16:03, Radim Vansa wrote: > > On 10/10/2014 02:38 PM, William Burns wrote: > >> On Wed, Oct 8, 2014 at 11:19 AM, Radim Vansa <rva...@redhat.com> wrote: > >>> Users expect that size() will be constant-time (or linear to cluster > >>> size), and generally fast operation. I'd prefer to keep it that way. > >>> Though, even the MR way (used for HotRod size() now) needs to crawl > >>> through all the entries locally. > >> Many in memory collections require O(n) to do size such as > >> ConcurrentLinkedQueue, so I wouldn't say size should always be > >> expected to be constant time or O(c) where c is # of nodes. Granted a > >> user can expect anything they want. > > OK, I stand corrected. Moreover, I was generalizing myself to all users, > > a common mistake :) > > > > Anyway, monitoring tools love nice charts, and I can imagine monitoring > > software polling every 1 second to update that cool chart with cache > > size. Do we want a fast but imprecise variant of this operation in some > > statistics class? > > > > Radim > > > >>> 'Heretic, not very well though of and changing too many things' idea: > >>> what about having data container segment-aware? Then you'd just bcast > >>> SizeCommand with given topologyId and sum up sizes of primary-owned > >>> segments... It's not a complete solution, but at least that would > enable > >>> to get the number of locally owned entries quite fast. Though, you > can't > >>> do that easily with cache stores (without changing SPI). > >>> > >>> Regarding cache stores, IMO we're damned anyway: when calling > >>> cacheStore.size(), it can report more entries as those haven't been > >>> expired yet, it can report less entries as those can be expired due to > >>> [1]. Or, we'll enumerate all the entries, and that's going to be slow > >>> (btw., [1] reminded me that we should enumerate both datacontainer AND > >>> cachestores even if passivation is not enabled). > >> This is precisely what the distributed iterator does. And also > >> support for expired entries was recently integrated as I missed that > >> in the original implementation [a] > >> > >> [a] https://issues.jboss.org/browse/ISPN-4643 > >> > >>> Radim > >>> > >>> [1] https://issues.jboss.org/browse/ISPN-3202 > >>> > >>> On 10/08/2014 04:42 PM, William Burns wrote: > >>>> So it seems we would want to change this for 7.0 if possible since it > >>>> would be a bigger change for something like 7.1 and 8.0 would be even > >>>> further out. I should be able to put this together for CR2. > >>>> > >>>> It seems that we want to implement keySet, values and entrySet methods > >>>> using the entry iterator approach. > >>>> > >>>> It is however unclear for the size method if we want to use MR entry > >>>> counting and not worry about the rehash and passivation issues since > >>>> it is just an estimation anyways. Or if we want to also use the entry > >>>> iterator which should be closer approximation but will require more > >>>> network overhead and memory usage. > >>>> > >>>> Also we didn't really talk about the fact that these methods would > >>>> ignore ongoing transactions and if that is a concern or not. > >>>> > >>>> - Will > >>>> > >>>> On Wed, Oct 8, 2014 at 10:13 AM, Mircea Markus <mmar...@redhat.com> > wrote: > >>>>> On Oct 8, 2014, at 15:11, Dan Berindei <dan.berin...@gmail.com> > wrote: > >>>>> > >>>>>> On Wed, Oct 8, 2014 at 5:03 PM, Mircea Markus <mmar...@redhat.com> > wrote: > >>>>>> On Oct 3, 2014, at 9:30, Radim Vansa <rva...@redhat.com> 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? > >>>>>> There was a lot of arguments in past whether size() and other > methods that operate over all the elements (keySet, values) are useful > because: > >>>>>> - they are approximate (data changes during iteration) > >>>>>> - they are very resource consuming and might be miss-used (this is > the reason we chosen to use size() with its current local semantic) > >>>>>> > >>>>>> These methods (size, keys, values) are useful for people and I > think we were not wise to implement them only on top of the local data: > this is like preferring efficiency over correctness. This also created a > lot of confusion with our users, question like size() doesn't return the > correct value being asked regularly. I totally agree that size() returns E > (i.e. everything that is stored within the grid, including persistence) and > it's performance implications to be documented accordingly. For keySet and > values - we should stop implementing them (throw exception) and point users > to Will's distributed iterator which is a nicer way to achieve the desired > behavior. > >>>>>> > >>>>>> We can also implement keySet() and values() on top of the > distributed entry iterator and document that using the iterator directly is > better. > >>>>> Yes, that's what I meant as well. > >>>>> > >>>>> Cheers, > >>>>> -- > >>>>> Mircea Markus > >>>>> Infinispan lead (www.infinispan.org) > >>>>> > >>>>> > >>>>> > >>>>> > >>>>> > >>>>> _______________________________________________ > >>>>> infinispan-dev mailing list > >>>>> infinispan-dev@lists.jboss.org > >>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev > >>>> _______________________________________________ > >>>> infinispan-dev mailing list > >>>> infinispan-dev@lists.jboss.org > >>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev > >>> -- > >>> Radim Vansa <rva...@redhat.com> > >>> JBoss DataGrid QA > >>> > >>> _______________________________________________ > >>> infinispan-dev mailing list > >>> infinispan-dev@lists.jboss.org > >>> https://lists.jboss.org/mailman/listinfo/infinispan-dev > >> _______________________________________________ > >> infinispan-dev mailing list > >> infinispan-dev@lists.jboss.org > >> https://lists.jboss.org/mailman/listinfo/infinispan-dev > > > > _______________________________________________ > infinispan-dev mailing list > infinispan-dev@lists.jboss.org > https://lists.jboss.org/mailman/listinfo/infinispan-dev >
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