Hello Sebastian, Something is really weird with this case, because it works at the local box. The most important question was whether the database statistics are calculated correctly (if not then execution plans would be wrong in the majority of queries). The direct comparison of statistical estimates and the real content of indexes has proven that statistics are accurate with factor from 0.5 to 2 for nearly all values, that is quite sufficient for the optimizer (logarithmic tolerance interval 0.7--1.3 is good enough when compared with scale from e.g. -3 to +10 ).
So I still do not know the exact origin of the problem and I should suspend the investigation for few days. Best Regards, Ivan Mikhailov OpenLink Software http://virtuoso.openlinksw.com On Thu, 2010-04-29 at 17:40 +0200, Sebastian Trüg wrote: > Hello, > > using a V6 server with default indexes I would like to know why the > following queries are different in performance. The store contains > thousands of different graphs but adding a "graph ?g {}" around all > patterns does not change the execution time. > > select * where { ?r a nfo:FileDataObject . > ?r nfo:fileName ?f . > ?f bif:contains 'breaking' . } > > takes a long time to finish - almost a minute. > > > select * where { ?r nfo:fileName ?f . > ?f bif:contains 'breaking' . } > > is finished in no time. > > I just would like to understand the reasons behind the difference. If > possible also a solution. :) > > Cheers, > Sebastian > > ------------------------------------------------------------------------------ > _______________________________________________ > Virtuoso-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/virtuoso-users
