I am evaluating a choice between Oracle OLAP and Pentaho Mondrian.
At the same time some people say that using a column DB could simply make the use of OLAP's redundant as they are much faster.
has anyone got any experience on the same. Will it help if ou OLAP sits on a column db ?
OLAP is not about the storage only; it is about the MDX language as well. MDX is much more powerful than SQL to handle multi-dimensional (with hierarchical dimensions) queries.
You can have a look to www.icCube.com - it's pretty fast - I mean no problem to aggregate let's say 30 millions of facts over 20 dimensions in sub-seconds (without any pre-aggregation computation).