I had a report that ran relatively slow in 8.2, but after it was moved to 8.4, it took several hours and did not finish. Has anyone else run into this issue, and/or does anyone else have any suggestions of what to look at? The report is exactly the same
Get your DBAs to check the SQL and compare the 2 reports. We have found the same reports on 8.2 run differently on 8.3. I guess 8.4 is the same, we have 8.4 but are using use for powerplay8 at the moment.
We found it was due to the path the SQL took in the FM model. We had to break an outer join on our model and it was fine.
Good luck