A never-ending query (almost)

I've got a curious problem I'd be interested in hearing any thoughts on. The machine is an HP9000/755 with HP-UX 9.01 and OnLine 5.01.UD1. The problem is with a table that has several indexes, including 1 on field1 and 1 on (field1, field2, field3, field4) (obviously I'm making up the column names). The table has approx. 1.5 million rows and is 1 table out of 550 or so in its particular database. A query of the form: select * from table where field1="xxx" comes back within a second or so. A query like: select * from table where field1="xxx" and field2="yyy" takes between <1 second to over an hour (!), depending on the value of field1. I've eliminated the obvious (at least, what's obvious to me): - tbcheck shows 4 extents - SET EXPLAIN shows that the index on field1 is being used in the first case and the composite index is used in the second (with an est. cost of 12 or so; apparently the statistics are OK). - npused is >0 (so it's not the 5.0 "negative npused" bug) - The problem persists even after dropping & recreating the table (so if an index is screwed up, Informix is managing to screw it up when it creates it). I've been unsuccessful at duplicating the problem under OnLine 7.1, so it's starting to look like an issue relating to 5.0. If anyone's seen something similar, I'd be very interested in hearing what you found. I'm willing to try almost anything short of recreating the database! Thanks... -- --- - Derrek (dirk@xmission.com)