Re: Optimizer's strategy

In article ehu@maicgn.SoftwareEngineering, ar@mai.de (Achim Reiners) writes: > >Hy everybody, > >I've some questions to the optimizer's strategy and to Informix' >plans regarding new versions. My current version is Online 5.01: > >1.) It is NOT possible to only look at the execution plan of a query > without really executing it. This feature (with SYBASE: set noexec on) > in my opinion is very important for tuning queries. > Now I nearly every time have to interrupt the query after some time > when running too long. > Question: Does Informix plan to implement this feature? Or is it already > implemented in Version 6.0 or 7.0 ? This NOT true. Simply $prepare'ing the statement without executing it will cause the query plan to be printed. Works for me in 5.02. >2.) I've learned that the Query-Optimizer internally works with selectivity > of the different parts of the query and compares them to find the best > way. But the output of SET EXPLAIN ON is quite poor. It only shows the > RESULTS of the comparison and it is NOT possible to imagine from this > output WHY this strategy is taken. > Question: Are there plans to improve and to detail the SET EXPLAIN output? The details on filter selectivity algorithms can be found in the Guide To SQL: Tutorial, P. 4-15. Simon