SE on DG-UX 5.4R2.01

Hi. We are using Informix SE on the DG Aviion 4605 running DG-UX 5.4 R2.01. We started encountering very very wild stuff after our database grew larger. One of the most frustrating issue is that the problem encountered doesn't happen on the DG-UX 5.4 with the same programs. The programs are written using 4GL/RDS, but problem also occurs when tested from ISQL. Below are listed the INFORMIX products we have with their release numbers. SQL 4.11.UC2 SE 5.01.UD2 R4GL 4.11.UC2 The problems we have seen are 1. A select statement which ran fine decided to go wild. With SET EXPLAIN ON the estimated cost of rows on the select was several hundred thousand. The database only had about 20,000 rows in it. The SQLEXEC did not die when the program was killed and carried on running wild until killed. After running an UPDATE STATISTICS the problem totally disappeared. After BCHECKing all the tables there were no corruptions. 2. An R4GL program that LOCKED EXCLUSIVE all the tables it used and only inserted into one of those tables crashed with Lock errors even though the table was locked. The crash occurred after 5,000 plus records were inserted. The program would crash but again the SQLEXEC would carry on running grabbing processing time and leaving all the tables in a LOCKED state. After killing the SQLEXEC the table was always then corrupted badly. By taking the insert out of a BEGIN work allowed the program to work OK. This problem could also be demonstrated by simply DELETING many rows from a table within ISQL. The number of UNIX locks was put up to 30,000 and the problem has gone away - for the moment. 3. A standard select statement of a few hundred rows was working fine. It then started to go wild. It does an order by but started to create 200 MB sort tables and eventually crashes on lack of disk space. The number of rows it selects is about 400 and the select is based on an 8 table select with one table having a self join. The order by has 7 char columns and one integer. This problem can be demonstrated within ISQL. If the number of tables selected is reduced to 5 plus one self join and the order by reduced to 6 columns the select will work within ISQL. But when run from within an R4GL program it will run but having processed all the rows will then continue to run until again a file gets so large that the disk space blows out. By running a DBEXPORT and DBIMPORT the problem may go away. However on one occasion this worked with in ISQL until an unrelated DELETE of a row from a different table altogether was run. When the SELECT was run again it again went wild. BCHECKing shows no errors on any tables in the database. Please help! We have been bugged by this problem for the last three weeks. Been notifying the Informix support, they recommended that the softwares were not compatible for the first order, which Informix shipped us the version 5.00 and 4.10 for the front end tools. We had since ordered the upgrade to version 5.01 and 4.11 for 4GL and ISQL. Thanks. Pls email SOS note to jesskung@solomon.technet.sg... Thanks in advance!