Query performance issue

Oracle 8.1.7.4 - Solaris 5.9 - Cost based optimizer

I have a query which takes 28 minutes to run on my production system and about a two minutes to run on my QA database.

The query looks like this:

Select ...
FROM

	siebel.W_ACTIVITY_F,
	siebel.W_REGION_D,
	siebel.W_LOV_D,
	siebel.W_DAY_D,
	siebel.W_PARAM_G
WHERE 
	W_ACTIVITY_F.REGION_WID = W_REGION_D.ROW_WID
AND 
	W_ACTIVITY_F.STATUS_WID = W_LOV_D.ROW_WID 
AND
	W_ACTIVITY_F.ACTUAL_START_WID = W_DAY_D.ROW_WID
GROUP BY 
	W_ACTIVITY_F.RESOLUTION_WID, 
	W_ACTIVITY_F.PRIORITY_WID, 
	W_ACTIVITY_F.CATEGORY_WID, 
	W_ACTIVITY_F.ACT_TYPE_WID, 
	W_ACTIVITY_F.STATUS_WID, 
	W_ACTIVITY_F.OWNER_WID, 
	W_ACTIVITY_F.REGION_WID, 
	W_DAY_D.CAL_YEAR,
	W_DAY_D.CAL_MONTH;

Explain plan (on both databases) looks like this:

| SELECT STATEMENT |
| 3M| 407M| 50788 | | |
| SORT GROUP BY |
| 3M| 407M| 50788 | | |
| HASH JOIN |
| 3M| 407M| 1658 | | |
| TABLE ACCESS FULL |W_DAY_D
| 11K| 149K| 15 | | |
| HASH JOIN |
| 3M| 359M| 1536 | | |
| TABLE ACCESS FULL |W_LOV_D
| 25K| 468K| 8 | | |
| NESTED LOOPS |
| 3M| 289M| 1292 | | |
| MERGE JOIN CARTESIAN |
| 645 | 13K| 2 | | |
| TABLE ACCESS FULL |W_PARAM_G
| 1 | 10 | 1 | | |
| SORT JOIN |
| 645 | 7K| 1 | | |
| TABLE ACCESS FULL |W_REGION_D
| 645 | 7K| 1 | | |
| TABLE ACCESS BY INDEX ROWID

|W_ACTIVITY_F   |     3M|  209M|      2 |      |      |            


|       INDEX RANGE SCAN

|W_ACTIVITY_F_F |     3M|      |      1 |      |      |    

(Note table W_PARAM_G contains only one row so the cartesian join is not
as bad as it sounds.)      

Row counts for w_day_d, w_lov_d, and w_region_d within 10% of each other on both databases.
The row count for w_activity_f is 3x10**6 on production and 2x10**6 on qa.

The 10046 trace for production lists 3x10**5 db file file sequential read waits while the trace for QA lists 2x10**4.

Would the 50% difference in the size of my w_activity_f table be sufficient to account for the 10-fold increase in the number of sequential read waits and the corresponding 10-fold difference in run time or should I be looking for hardware or other issues?

Thanks,
Peter Schauss   

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