Glory to our holy Leo for transmitting *brahmavidya* to shishya !!
Turning back to this optimization problem, this might be trickier since
execution time does not seem to behave linearly. For instance, consider
declare function local:test1($i){let $data_3 as item() *:= fn:for-each((1
to 1000000*$i), function($a_0) as item()? { (2 * $a_0) }) return for $n in
(1 to 2) return fn:count($data_3)};
declare function local:test2($i){count(fn:for-each((1 to 1000000*$i),
function($a_0) as item()? { (2 * $a_0) }))};
Then execution time is ( the results are stable while repeating the
experience )
prof:time(local:test1(7)) : 631.32 ms prof:time(local:test2(7)) : 451.32 ms
prof:time(local:test1(8)) : 2550.17 ms prof:time(local:test2(8)) : 507.32
ms
2015-01-13 22:43 GMT+01:00 Christian Grün <christian.gr...@gmail.com>:
> Hi Jean-Marc,
>
> beforehand: The first issue you reported back to us recently [1] has
> been fixed by our functional guru Leo! A new snapshot is available
> [2].
>
> > Hi. Thanks for the FLWOR trick, behaving in constant time. However it
> seems
> > to generates an unexpected 5X time overhead
>
> Most probably this is because the results of for-each will be cached,
> while in the previous case (if no inlining takes place), all items
> will be iterated.
>
> Hope this helps,
> Christian
>
> [1] https://github.com/BaseXdb/basex/issues/1052
> [2] http://files.basex.org/releases/latest/
>
>
> On Tue, Jan 13, 2015 at 9:19 AM, jean-marc Mercier
> <jeanmarc.merc...@gmail.com> wrote:
> > Christian,
> >
> > Hi. Thanks for the FLWOR trick, behaving in constant time. However it
> seems
> > to generates an unexpected 5X time overhead, and I can't use it
> > straightforwardly as workaround. Can you reproduce it, since this
> overhead
> > might be due to eclipse ?
> >
> > declare function local:test(){fn:for-each(1 to 10000000,
> > function($a){2*$a})};
> > declare function local:test1(){count(local:test())};
> > declare function local:test2(){let $ data := local:test() return for $n
> in
> > (1 to 10) return count($data)};
> >
> > prof:time(local:test1()) ouput : 639.12 ms
> > prof:time(local:test2()) ouput : 2431.67 ms
> >
> >
> >
> > 2015-01-13 1:59 GMT+01:00 Christian Grün <christian.gr...@gmail.com>:
> >>
> >> Hi Jean-Marc,
> >>
> >> interesting one; it seems that $data is inlined and thus evaluated
> >> more than once. This doesn't happen if a FLWOR expression is used:
> >>
> >> let $data := fn:for-each ...
> >> for $n in 1 to $i
> >> return local:test2($data, $n)
> >>
> >> Should be easy to resolve.
> >>
> >> Thanks for your (always concise) examples,
> >> Christian
> >>
> >>
> >> On Mon, Jan 12, 2015 at 9:08 PM, jean-marc Mercier
> >> <jeanmarc.merc...@gmail.com> wrote:
> >> > Hello,
> >> >
> >> > I am facing some performances issues, probably due to unexpected query
> >> > reevaluation. Might it be due to the optimizer ? Here is a code to
> test
> >> >
> >> > declare function local:test($i){
> >> > let $data := fn:for-each(1 to 10000000, function($a){2*$a} )
> >> > (: let $data := xquery:eval("fn:for-each(1 to 10000000,
> >> > function($a){2*$a} )") :)
> >> > return (1 to $i) ! local:test2($data,.)
> >> > };
> >> >
> >> > declare function local:test2($data, $dummy) { count($data) };
> >> >
> >> > (1 to 10) ! prof:time(local:test(.))
> >> >
> >> > Output :
> >> >
> >> > 683.76 ms
> >> > 1137.95 ms
> >> > 1727.68 ms
> >> > 2151.06 ms
> >> > 2694.84 ms
> >> > 3189.57 ms
> >> > 3725.1 ms
> >> > 4277.51 ms
> >> > 4815.74 ms
> >> > 5417.79 ms
> >> >
> >> > Note that using xquery:eval (toggling the comment inside local:test).
> >> > seems
> >> > to perform correctly. However I can't use this trick as a workaround.
> >> >
> >> > (1 to 10) ! prof:time(local:test(.))
> >> > Ouput :
> >> >
> >> > 2472.71 ms
> >> > 825.61 ms
> >> > 3013.14 ms
> >> > 986.81 ms
> >> > 2982.97 ms
> >> > 778.24 ms
> >> > 1195.33 ms
> >> > 3280.7 ms
> >> > 976.96 ms
> >> > 913.69 ms
> >
> >
>
