>Have you tried adding a FLUSH statement?

No, hadn't tried that - but according to Hacker's Guide, this can degrade performance - but more to the point, the primary table is read-only, so I'm not writing anything to disk here - at least not intentionally :) The cursor should fit in memory. I kind of have the impression that at some point the primary table starts taking up too much memory and forcing the cursor to disk, but I don't know why or how to resolve it...