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  3. June 2005

Re: Using Visual Explain in Iseries Navigator ?

I believe you're looking at the result of running qqqoptim, one of those mythic programs that's so complex there is nobody alive who can truly understand it. It creates the access plan that is used by all queries. One of the things it considers is the available indexes and/or access paths. However, it also considers a lot of other things, like are you currently running in an interactive job? (Yes? return the first page of results quickly. No? run the query to completion in the shortest possible time), how many rows are in the table in question? (More than <some magic figure>? Expend the resources to find an access path. Otherwise, use sequential access) What is the cardinality of the keys? What is the available index type? (B-Tree and cardinality outside of acceptable norms?) and lots of other stuff that I know even less about than the blather I just wrote. The debug message has a disclaimer that's something along the lines of "Even if you do what I asked you for, I may not use your index because I know more about it than you do." Is the response time acceptable? If so, I recommend accepting that it really does know what it's doing. If you need 50 rows of data and it's taking an hour and a half, call level 1. Developers must enjoy working on problems with qqqoptim almost as much as we mortals would enjoy sliding barefoot down the edge of a 50 ft razor blade, but, at least in my experience, they're very competent, they try very hard, and eventually do get things working correctly.

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