How do add primary key contraint on existing table?

Hello all, I have to periodically purge data from an approximately 7 million row table. Btw, I am running Informix OnLine 7.20 on a DEC Alpha Unix 3.20G with 128 MB. The table is fragmented over two dbspaces. I am doing the purge by unloading all data except that which I want to exclude, then using dbload utility to reload the data after dropping the table. Prior to dropping the table, I run the dbschema utility with server specific syntax so I can recreate the table. The table has two not null constraints on it along with a primary key constraint. I have found that I can load 40,000 records per minute without the primary key, and 5000 records/min with the primary key constraint. That works out to 3 hours vs 29 hours. I tried to use the ALTER TABLE command (without specifying the dbspace) to add the primary key constraint after loading the data, but I get an ISAM error message that says it has run out of disk space. My question is this: does the ALTER TABLE command try to create a new table in the same dbspace (and then copy records from old to new and then drop old table)? If so, it would definitely run out of space; what syntax would I use to specify that I want to add the contraint in-place? If not, where is the system trying to add the constraint, and how can I get it on there without running out of space? Any help would be greatly appreciated... John Graffio Systems Manager, CPTC (714) 637-9191 x202