20.04.2017 17:50, Dimitry Sibiryakov wrote: > 20.04.2017 16:20, Vlad Khorsun wrote: >>> even in the simplest cases like "select f from t1 union select f from t2"? >> This case nor simplest nor better for parallel execution than "ordinary" >> "select * from t". > > Union used to produce plan SORT (T1 NATURAL), SORT(T2 NATURAL). Both > record streams can > be fetched and sorted in parallel and then merged, right? And because of > selects from > different tables, they won't race on data pages.
No. This is very naive view on parallel query execution. Real implementations works differently. There is a lot of info in the net about it. Vlad ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot Firebird-Devel mailing list, web interface at https://lists.sourceforge.net/lists/listinfo/firebird-devel
