On Wed, Oct 8, 2014 at 6:19 PM, Radim Vansa <[email protected]> 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. > They might expect that, but there is nothing in the Map API suggesting it. > > '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). > We could create a separate DataContainer for each segment. But would it really be worth the trouble? I don't know of anyone using size() for something other than checking that their data was properly loaded into the cache, and they don't need a super-fast size() for that. > > 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). > Exactly, we need to iterate all the entries from the stores if we want something remotely accurate (although I had forgotten about expiration also being a problem). Otherwise we could just leave size() as it is now, it's pretty fast :) > > 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 <[email protected]> > wrote: > >> On Oct 8, 2014, at 15:11, Dan Berindei <[email protected]> wrote: > >> > >>> On Wed, Oct 8, 2014 at 5:03 PM, Mircea Markus <[email protected]> > wrote: > >>> On Oct 3, 2014, at 9:30, Radim Vansa <[email protected]> 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 > >> [email protected] > >> https://lists.jboss.org/mailman/listinfo/infinispan-dev > > _______________________________________________ > > infinispan-dev mailing list > > [email protected] > > https://lists.jboss.org/mailman/listinfo/infinispan-dev > > > -- > Radim Vansa <[email protected]> > JBoss DataGrid QA > > _______________________________________________ > infinispan-dev mailing list > [email protected] > https://lists.jboss.org/mailman/listinfo/infinispan-dev >
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