Hi Jörg, You're right about the very naive behaviour of that method. It could _certainly_ use an optimization or two. I can only speak for myself, but I just never used MetaModel much for joins and thus never gave it much thought. Looking at the code I'm thinking that we can do much better.
Would you be interested in working on improving this condition? If so I will happily share insights and ideas on how we can pull it off. Cheers, Kasper 2016-05-01 4:12 GMT-07:00 Jörg Unbehauen < [email protected]>: > Hi all, > > we just tried out metamodel with mongodb and tried out a simple join (as > in select * from t1 join t2 on (t1.id = t2.oid) ) between two collections > each containing roughly 10,000 documents. Using a developer setup on a mac, > we did not get a result, as the system was more or less stuck. > A quick examination revealed that > MetaModelHelper.getCarthesianProduct(DataSet[] fromDataSets, > Iterable<FilterItem> whereItems) consumes most of the resources. > This implementation first computes the carthesian product in memory and > than applies filters on it. > I wonder what the rationale behind this implementation is, as it will not > scale well, even for selective joins. > Or am i using Metamodel wrong here, as in: The join should never be > computed by getCarthesianProduct(). > > The problem appears to me as a general one, i did not supply a code > example. > > Best, > > Jörg > > >
