[Monetdb-developers] problems with XQuery aggregation

Stefan Manegold Stefan.Manegold at cwi.nl
Thu Oct 25 14:39:31 CEST 2007


Henning,

I suppose you use the default MPS ("milprint_summer") backend, right?
(i.e., a simple `mclient -lxquery q.xq` or `pf [-M] q.xq | mclient -lmil`.)

Could you please also try the algebra backend via
	`pf -A q.xq | mclient -lmil`
and report the results/behaviour?

Stefan

On Thu, Oct 25, 2007 at 12:39:07PM +0200, Henning Rode wrote:
> hej monetdb developers,
> 
> i tried to write a simple aggregation query:
> 
> let $cands := doc("x.xml")//c
> for $eid in distinct-values($cands/@id)
> return <candidate id="{$eid}" count="{count($cands[@id eq $eid])}"/>
> 
> however, executing the above query turns out to be rather difficult. i
> always killed the process after waiting for more than half an hour
> without getting any result.
> 
> x.xml is 17MB large and contains 300000 candidates nodes c.
> i run it on Monet Database Server V4.19.0 where the query crashed
> 
> ERROR = !ERROR: GDKload: cannot mmap(): name=10/1030, ext=buns.priv
>         !OS: Cannot allocate memory
>         !ERROR: GDKload failed: name=10/1030, ext=buns.priv
>         !ERROR: CMDleftjoin: operation failed.
> 
> and on the newer stable release MonetDB Server v4.20.0 on a machine with
> 16GB memory where the query just runs endless.
> 
> apparently the query compiler does not recognise the necessary join and
> aggregation here. is that a known problem?
> 
> btw. sorting the candidates by @id value is done in seconds:
> 
> let $cands := doc("x.xml")//c
> for $c in $cands
> order by $c/@id
> return $c
> 
> best -henning
> 
> 
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-- 
| Dr. Stefan Manegold | mailto:Stefan.Manegold at cwi.nl |
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