Re: [infinispan-dev] default value for virtualNodes

Good stuff! Thanks for this. Yes, I'm ok with numVirtualNodes=48 as a default. Galder, your thoughts from a Hot Rod perspective? On 27 Jan 2012, at 08:41, Dan Berindei wrote: > Hi guys > > I've been working on a test to search for an optimal default value here: > https://github.com/danberindei/infinispan/commit/983c0328dc40be9609fcabb7... > > I'm measuring both the number of keys for which a node is primary > owner and the number of keys for which it is one of the owners > compared to the ideal distribution (K/N keys on each node). The former > tells us how much more work the node could be expected to do, the > latter how much memory the node is likely to need. > > I'm only running 10000 loops, so the max figure is not the absolute > maximum. But it's certainly bigger than the 0.9999 percentile. > > The full results are here: > http://fpaste.org/cI1r/ > > The uniformity of the distribution goes up with the number of virtual > nodes but down with the number of physical nodes. I think we should go > with a default of 48 nodes (or 50 if you prefer decimal). With 32 > nodes, there's only a 0.1% chance that a node will hold more than 1.35 > * K/N keys, and a 0.1% chance that the node will be primary owner for > more than 1.5 * K/N keys. > > We could go higher, but we run against the risk of node addresses > colliding on the hash wheel. According to the formula on the Birthday > Paradox page (http://en.wikipedia.org/wiki/Birthday_problem), we only > need 2072 addresses on our 2^31 hash wheel to get a 0.1% chance of > collision. That means 21 nodes * 96 virtual nodes, 32 nodes * 64 > virtual nodes or 43 nodes * 48 virtual nodes. > > Cheers > Dan > > > On Fri, Jan 27, 2012 at 12:37 AM, Sanne Grinovero <sanne(a)infinispan.org&gt; wrote: >> On 26 January 2012 22:29, Manik Surtani <manik(a)jboss.org&gt; wrote: >>> >>> On 26 Jan 2012, at 20:16, Sanne Grinovero wrote: >>> >>> +1 >>> Which default? 100? A prime? >>> >>> We should also make sure the CH function is optimized for this being on. >>> >>> >>> Yes, we should profile a session with vnodes enabled. >> >> Manik, we're using VNodes in our performance tests. The proposal is if >> we can provide a good default value, as the feature is currently >> disabled by default. >> >> Cheers, >> Sanne >> >>> >>> >>> -- >>> Manik Surtani >>> manik(a)jboss.org >>> twitter.com/maniksurtani >>> >>> Lead, Infinispan >>> http://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 > _______________________________________________ > infinispan-dev mailing list > infinispan-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/infinispan-dev -- Manik Surtani manik(a)jboss.org twitter.com/maniksurtani Lead, Infinispan http://www.infinispan.org _______________________________________________ infinispan-dev mailing list infinispan-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/infinispan-dev