Performance - Informix Se 7.22

We have recently upgraded SE from SE V5.04 to SE 7.22. At the same time HPUX was upgraded from 9.04 to 10.10. Since then, all queries running on the large sales history tables are running about 12X slower. The problem appears to be related to the creation of temphash overflow files in DBTEMP. I have tried 1) update statistics with all its flavours ( High, low, Medium ), 2) Re-writing the query to force different access plans 3) Drop and Re-create of the tables involved 4) All related HP-Ux Informix patches - Even those for on-line 5) Sort the lookup tables by their primary index 6) Removing the order by from the select My sample query is a three table join between 1) Sales History (SH) - 1 Million rows, Record Size 1728 Bytes 2) Item (IT) - 5,000 Rows, Record Size 480 Bytes 3) Customer (CU) - 9,000 Rows, Record Size 650 Bytes The Access plan is essentialy 1) Sequential Scan Customer 2) Index Read to Sales History on customer 3) Index Read to Item on item The query basically sums sales by customer and Item Group ( on the Item Table ).i.e. select SA.div_code, CU.terr_code, SA.cust_num, SA.ship_num, IT.sa_item, sum(SA.sales_1), sum(SA.sales_2) ... sum(SA.sales_12) from customer CU, sales_hist SA, item IT where blah, blah The system almost immediately creates 5 temphash overflow files in DBTEMP and spends approximately 50 minutes populating these files. The system then spends the next 12 hrs spinning through these five temphash overflow files creating a srt file. It is only with a group by and sum, that the temphash overflow files are created. Any in-sight into what creates these files and how they can be prevented would be greatly appreciated. Tom