On Thu, Feb 18, 2010 at 07:40:15PM +0100, Stefan de Konink wrote: > Op 18-02-10 19:22, Stefan Manegold schreef: > >"It" (in fact we) choose to do a hash select, and since there is no hash > >table, yet, we need to build it, which is infact more expensive than a > >simple scan select for this very operation (later operation *might* then > >benefit from the hash table ...): > > Question about that then; if we make an on the fly hash. Why isn't > it 'maintained' between queries (or does this depend on the chosen > pipeline?) Because the query doesn't seem to get faster when running > it multiple time?
because it is built on an intermediate result (base BAT plus delta BATs applied) that is gone, again after the query has been executed. Stefan > >For now, you can just locally disable/remove that alternative in the above > >code, > >try again, and report the result. > > Cold: > sql>select kvk from kvk where kvk = 412657690010; > +--------------+ > | kvk | > +==============+ > | 412657690010 | > +--------------+ > 1 tuple > Timer 1174.737 msec 1 rows > > Hot: > sql>select kvk from kvk where kvk = 412657690010; > +--------------+ > | kvk | > +==============+ > | 412657690010 | > +--------------+ > 1 tuple > Timer 23.741 msec 1 rows > sql>select kvk from kvk where kvk = 412657690010; > > > Thanks for this 20x performance increase! (And it gets even better, > because numbers that doesn't exist are excluded in ~13ms.) > > > Stefan > -- | Dr. Stefan Manegold | mailto:[email protected] | | CWI, P.O.Box 94079 | http://www.cwi.nl/~manegold/ | | 1090 GB Amsterdam | Tel.: +31 (20) 592-4212 | | The Netherlands | Fax : +31 (20) 592-4199 | ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Monetdb-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/monetdb-developers
