Hi Martin, I did say "not", so we are saying the same thing.
I like that QM is smart about it. Best regards, Henry Henry P. Unger Hitech Systems, Inc. http://www.hitech.com -----Original Message----- From: u2-users-boun...@listserver.u2ug.org [mailto:u2-users-boun...@listserver.u2ug.org] On Behalf Of Martin Phillips Sent: Thursday, July 16, 2009 12:36 PM To: U2 Users List Subject: Re: [U2] Universe Retrieve Hi Henry, > I was under the impression that an EVAL calls the same compiler > that an I-type does, and that any expression optimization would be > done therein. As far as I know, EVAL does indeed call the same compiler. As I think you realise, the point is that an I-type expression such as 1: I 2: SPACE(3) (which I have seen used to get differing column spacings) will compile to a pcode sequence that produces a string of three spaces. This does not tell us how the query processor will then go on to use it. A "normal" I-type expression, whether from the dictionary or from use of EVAL, would be executed for each occurrence of it in the report, typically once per record. In the case of my spacing expression above, the query processor would actually only need to evaluate the expression once and then drop it into the report as a constant item. I think that this is what the original poster was asking about. I have no idea whether UV does this (QM does). Your experiment seems to tell us..... > Here are some empirical results using UniVerse 10.2.7: > >>TIMEIT 50 COUNT VOC WITH F1 = 'V' > COUNT VOC WITH F1 = 'V' > Elapsed 1.3006 > >>TIMEIT 50 COUNT VOC WITH F1 = EVAL "'V'" > COUNT VOC WITH F1 = EVAL "'V'" > Elapsed 5.135 > > This suggests that the query processor does not detect that the result of > the evaluation is a constant and optimize its execution. No, I think that this is actually showing the opposite. The query was considerably faster where your test was a simple literal WITH F1 = 'V' whereas the EVAL expression added a further four seconds to your query. If the query processor detected that EVAL "'V'" was a constant and optimised it I would expect both queries to take the same time. It does look as though it is evaluating the expression for every record. Martin Phillips Ladybridge Systems Ltd 17b Coldstream Lane, Hardingstone, Northampton, NN4 6DB +44-(0)1604-709200 _______________________________________________ U2-Users mailing list U2-Users@listserver.u2ug.org http://listserver.u2ug.org/mailman/listinfo/u2-users _______________________________________________ U2-Users mailing list U2-Users@listserver.u2ug.org http://listserver.u2ug.org/mailman/listinfo/u2-users
