Informix 7.1 Online -- Technical Question

Hi, I wrote an article about a week ago asking some questions about Informix 7.1 performance, and whether the system could be processor-bound. I'm using an RS/6000 running AIX 3.1.2 with 128MB of RAM, and a Shared memory ceiling of 50MB. I'm developing a model of how our system performs given different client configurations, and have found that the system is indeed processor bound. So, progressing heartily ahead, I came up with a formula that I thought would express the amount of work that the Informix database was doing for each update to the database tables that we perform, and used this formula to predict the number of CPU seconds Informix would require to process our data. This model has proven very accurate. I use the assumption that each insertion into the databases incurs a cost roughly equivalent to the LOG of the number of rows in the table (this follows naturally from my assumption that the depth of the tree which is index searched is logarithmic with respect to the number of elements in the table). BUT, what I have learned through using "oncheck -pT", is that most of our tables have indices of DEPTH 3, (indicating a very large number of keys in each tree level) Given this, I would expect that the amount of time to find the item in the index would be roughly constant, assuming the next node traversed in the index tree is chosen by a constant time hash function, or some such. The burning question then, to Informix personnel, gurus, or anyone, is : WHY would the amount of time to perform an operation on a table vary with the logarithm of the number of rows, if the indexes used to search the tree are roughly the same depth? Am I missing something here? Is there another process involved that is O(logn) ?? Thanks for any help in advance, Scott Miller Siemens Rolm Communications