2012/1/9 Thomas Mueller <[email protected]> > Hi, > > > > Why do you multiply the costs to the level tree nodes? > > Because I think that's the right way to do it. Maybe it's wrong. If you > have an example where it's wrong and have a better solution then please > tell me! > > I'm not saying this is wrong! As I said, I'm trying understand the query planner, cost model and so on. A example of information I'm searching is available here<http://db.apache.org/derby/docs/10.8/tuning/tuning-single.html>.
> > > Do you use histogram to make some predictions? > > Currently, histograms are not used, only the index (column) selectivity. > And the join selectivity, I found nothing in the code about it. There is a mechanism (plans) to address this? Another thing is the planner to query with more than 7 joins (Cost based optimizer, using a genetic algorithm for complex queries, zero-administration). This isn't a critic, just a observation: I think the algorithm isn't a genetic optimizer. The genetic algorithms are described in the literature as optimizers based in the Darwin's theory with features like: selection, crossover, mutaion and so on. The Genetic algorithm of H2 seems to me like a random walk in the search space. The algorithm could be thought of as part of a genetic algorithm, specifically mutation operator. -- You received this message because you are subscribed to the Google Groups "H2 Database" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/h2-database?hl=en.
