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

[Scott Klement <rpg400-l@xxxxxxxxxxxxxxxx>]

> 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