First Thanks to all your answer it's help to really check all the aspects.
- In fact the system we want to build have to manage a lot of data but not in an heavy transactional way. Solr can handle the data but doesn't have the distributed way to serve it. But it's always possible to just duplicate the data in my case. then we can load balancing the queries between multiple instance server. - We load a large set of data once a week and that all this data are going to be used as his without modification or update or delete. In this point load the data into Solr is very easy because we make a csv file and that's it it's inside. - The data need to be structured but not like a relational database. Obviously Solr doesn't fit the data structure required. it force us to de-normalize a lot of data and build like a very very big table it's force us also to build very difficult lucene query. - The speed to query for data is critical cause the application is internet oriented we hope a lot of queries / minutes. With this point the problem is that with the same amount of data Solr have been faster than cassandra but of course the data structure is not the same. It seems by the end we'll go as Tatu tell to have an hybrid solution mixing Solr and Cassandra. I'm not sure its the best in our case Thanks
