oh, amazing...
with the algebra backend it works in seconds.
thanks a lot. is MPS not able to create an efficient query plan here?
-henning
Stefan Manegold wrote:
> 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([EMAIL PROTECTED] 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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