SQL statement performance in DW environment

My data warehousing application has a fact table containing 10 million records. The table schema is as follows - iteration_id int /*used to access information for a specific iteration*/ distribution_entity_id int
...
...

oem_revenue number /* field storing metric information */ <160 other different number fields holding metric information>

Most of the table access is via iteration_id.The table is partitioned using iteration_id so that specific parition can be hit directly if the query references an iteration number e.g. iteration_id = 2075

Sample query -
SELECT distribution_entity_id,sum(nvl(oem_revenue,0)) FROM ods_facts
WHERE iteration_id = 2075
group by distribution_entity_id

At times single iteration is so large that it hits 0.4 million records. So in those cases the above query has very poor performance. Is there any way to improve the performance other than creating aggregate table(s) ? Any insight is appreciated .
Thanks
Abhijit Bhattacharya

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