OLAP taking 5 time more space than RDBMS?

Question

Hello,
I have been investigating Oracle's OLAP capabilities for about 2 weeks now in an effort to determine whether OLAP would be a feasible solution for my company's data warehousing needs.
I have created an extremely simple analytic workspace that is based on a single relational fact table. The fact table contains both the dimension values (integers) and the measuers (floats). There are a total of about 300,000 dimension values all of which reference measures (the data is perfectly dense).
I created a dimension and a data cube using the Enterprise Manager OLAP interface. Next, I created the analytic workspace using the Analytic Workspace Manager wizard. This AW building step took an extraordinary amount of time considering the simplicity of the data. In fact, I started it on a Friday afternoon, monitored it for about 2 hours, and it still hadn't finished, so I let it run over the weekend (for this reason, I am not sure how much time exactly it took, but it's definitely quite a few hours). Is this normal? Copying the relational table takes 10 seconds, and I find it hard to believe that building an AW with the same data would take so much time.
Finally, coming back on Monday I see that the AW was created successfully. I went into the tablespace map to look at how big the binary blob is. To my great surprise, the AW was taking up about 5 times more extents than my relational table (contrary to what I've read so far about OLAP and its supposedly very storage-efficient data cubes).
I was wondering if anybody could advise me on what I could have done wrong and/or inefficiently? Am I missing something here, or is OLAP really consuming much more space comapred to relational tables?
Thanks!
Dobo Radichkov

Answer 1

Gotcha.
Well, here are a few ideas:
1) There is a bug in the 9i OLAP where dimension loads take WAY too long. I have a dimension with approx 77,000 members. On 9i, it took hours to load. On 10g 10.1.0.3 it loads in under 1 minute. You might want to open a TAR, the bug was something about one of the patch sets not being applied right
2) From a space standpoing, I wouldn't worry about this too much. When the AW wizard creates an "empty" workspace, it already has lots of items in it that support the metadata, etc. Also, there is the concept of "free pages" that get allocated but end up not being used (they are "temp")
To check this out, attach your AW and then fire up the OLAP worksheet. To see "free" pages vs. "used" pages, do the following:
show aw(pages)
show aw(freepages)
One last thing you can do, to see the size of all items in the AW:
attach AWname ro first
limit name to all
sort name d obj(disksize)
rpr w 40 obj(disksize)
This will show the "relative" size of the items, I think in "pages" (to see how big a page is just do a
show aw(pagesize)
Hope this helps!