Re: I'd be interested in a discussion on the topic of LOOKUP vs. %LOOKUP -- RPG400-L

There are two ways to check the array that I am aware of. LOOKUP and %LOOKUP. The difference in performance appears to be a factor of 10. Is that to be expected in your opinion? Can LOOKUP take 25 minutes to run, and %LOOKUP take 4 minutes?

Depends on how you're using %LOOKUP. If you're using it on an array that's been sorted, and has the "ASCEND" or "DESCEND" keyword coded on the array definition, then you're doing a binary search lookup -- in which case it doesn't surprise me one bit that %LOOKUP is 10 times faster than LOOKUP.

The LOOKUP op-code (or %LOOKUP without ASCEND/DESCEND/SORT) is the same thing (more or less) as looping through the array (with a DO or FOR loop) and checking each array element to see if it matches. Much slower.


Of course, %LOOKUP won't compile to V4R2 anyway.
So, what say you?  How to solve this pig of a performer?

If you want to continue to use an array, you could consider using the bsearch() API (from the ILE C runtime library) it'll perform similarly to the way %LOOKUP works.

Otherwise, consider at least trying using an indexed access method, such as a database file w/CHAIN operation, or a user index. Although they require disk access, which will slow it down, the algorithm for a keyed lookup is much smarter than a linear "loop through all the elements" type search operation. Of course, YMMV... Sometimes it'll be faster, sometimes it wont.

HTH

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