On Thu, Oct 25, 2007 at 02:44:44PM +0200, Henning Rode wrote:
oh, amazing... with the algebra backend it works in seconds.
thanks a lot. is MPS not able to create an efficient query plan here?
apparently.
Stefan
-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="{$eid}" count="{count($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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