I am a stupid (was Online Performance Degradation)

Now that I have had some sleep, I realize that I should expect logN behaviour: if the number of adds/minute falls off as log(t), then the time for each add increases as log(t), which we are obviously never going to better. Several people have commented that the solution is to drop the indexes, do the adds, and then rebuild the indexes. Unfortunately I cannot do this, as the adds come in unpredictably, and other processes will be doing lookups at all times. So it appears that Informix is doing a wonderful job, and there is nothing else to be done. I think I will try to precisely characterize the curve, just to make sure logN is in fact correct. Thanks to all who responded, Andrew Shaw AT&T Bell Labs