Re: Cost Vs. Rules Based Optimisers

• anewson_at_cix.compulink.co.uk ("Alastair Newson") wrote: At the UK OUG conference there was a technical lesson/session with Chris Ellis, who knows the optimiser very well. He went on record as stating that with v7.1.3 he thinks the cost based optimiser will always at least as well a programmer. This is the first release that he has been willing to recommend using the cost based optimiser over the rule based.
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we're on 7.1.3.4.0 on VMS 6.1, so your statement encouraged me to try the cost-based optimizer again. my first experiences with it were entirely negative.

well, i just ran a very limited test on a piece of code that i did not NOT try to optimize under rule-based. so far i am not impressed. the

cost-based optimized code seems to be as slow or slower that the
rule-based optimized code.  in one case, it took 5 minutes of cpu with
cost-based vs 2 minutes of cpu using rule-based.  in another case, the
cost-based used the same cpu, but did improve the i/o considerably.  i'm

i'm also bothered by the lack of documentation on the cbo. i use a lot of views based on views based on .... etc. i've yet to see any clear guidance on how to use hints in this type of situation, or whether they can be used in views at all. Received on Mon Feb 20 1995 - 17:38:36 CET