Database is extremely slow

I have an Oracle 7.3.4.4 database that is experiencing extremely slow response times in the past few days. I know that one of the tables had as many as 3,000,000 rows, but over the past week some of the information has been purged, so now there are about 2,200,000 rows; other tables have also been drastically reduced in row count. Last night, I updated statistics (hoping it might make a difference), but unfortunately, we don't observe any real difference.

I have two questions:

1. The Optimizer_Mode parameter for Oracle is set to RULE. Does this mean that the server does not rely on statistics stored in the catalog when it is putting together the execution plan for a query? I am considering changing this to CHOOSE. Can I do this without having an adverse effect on performance or changing query results?
2. Should I go ahead and rebuild the indexes on the tables that I know have been radically reduced in row count?

This system has never performed well, it is running on older, obsolete hardware and software, and a replacement system for it has been targeted and is being tested as I write this, but does anyone out there have any specific recommendations that I could try to help our current situation?

Thanks,

Scott Ashby
DBA
Swedish Match North America Received on Wed Jun 25 2003 - 07:53:49 CDT