On Sunday, January 26, 2014, Tom Lane <t...@sss.pgh.pa.us> wrote: > Jeremy Harris <j...@wizmail.org <javascript:;>> writes: > > In ordered_set_startup() sorts are initialised in non-randomAccess mode > > (tuplesort_begin_heap() and ~datum(), last argument). > > > The use of tuplesort_skip_tuples() feels very like a random access to > > me. I think it doesn't fail because the only use (and implementation) > > is to skip forwards; if backwards were tried (as the interface permits) > > external sorts would fail because multiple tapes are present for > > FINALMERGE. > > Well, we certainly don't want to incur the overhead of randomAccess mode > when we're not actually going to use it, so I'd resist changing the code > in ordered_set_startup(). > > It's true that if tuplesort_skip_tuples() supported backwards skip, it > would need to insist that randomAccess mode be enabled *when a backwards > skip is used*. But such a feature is purely hypothetical ATM. > > >
+1 In ordered set functions, we normally don't skip backwards and skip tuples while sorting in,for e.g. Hypothetical set functions in only a forward manner. -- Regards, Atri *l'apprenant*
