Re: [infinispan-dev] About size()

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 <rvansa(a)redhat.com&gt; 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 <mmarkus(a)redhat.com&gt; wrote: >>>>> On Oct 8, 2014, at 15:11, Dan Berindei <dan.berindei(a)gmail.com&gt; wrote: >>>>> >>>>>> On Wed, Oct 8, 2014 at 5:03 PM, Mircea Markus <mmarkus(a)redhat.com&gt; wrote: >>>>>> On Oct 3, 2014, at 9:30, Radim Vansa <rvansa(a)redhat.com&gt; 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(a)lists.jboss.org >>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev >>>> _______________________________________________ >>>> infinispan-dev mailing list >>>> infinispan-dev(a)lists.jboss.org >>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev >>> -- >>> Radim Vansa <rvansa(a)redhat.com&gt; >>> JBoss DataGrid QA >>> >>> _______________________________________________ >>> infinispan-dev mailing list >>> infinispan-dev(a)lists.jboss.org >>> https://lists.jboss.org/mailman/listinfo/infinispan-dev >> _______________________________________________ >> infinispan-dev mailing list >> infinispan-dev(a)lists.jboss.org >> https://lists.jboss.org/mailman/listinfo/infinispan-dev _______________________________________________ infinispan-dev mailing list infinispan-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/infinispan-dev