Hi Mirko,
Running similar queries with ORDER BY and LiMIT query modifier against my
Virtuoso 5.0.12 build and do not observe the behaviour you report. What
Virtuoso release are you testing against ?
Also, can you provide the output of running the explain () function which
describes the query compilation and may provide some indication as to why the
query with 2 graphs is taking so long, see:
http://docs.openlinksw.com/virtuoso/fn_explain.html
Note you will need to run this command using the isql command line query tool
and prepend them with the "SPARQL" keyword for execution, as :
explain(' SPARQL SELECT ?description FROM <http://localhost/graphA> WHERE {
?recource <http://purl.org/dc/terms/subject> <http://localhost/someElement> .
?recource <http://purl.org/dc/terms/subject> ?relatedElement . ?relatedElement
<http://purl.org/dc/terms/description> ?description . ?relatedElement
<http://localhost/score> ?score } ORDER BY DESC (?score) LIMIT 4');
query B (times out):
explain(' SPARQL SELECT ?description FROM <http://localhost/graphA> FROM
<http://localhost/graphB> WHERE { ?recource <http://purl.org/dc/terms/subject>
<http://localhost/someElement> . ?recource <http://purl.org/dc/terms/subject>
?relatedElement . ?relatedElement <http://purl.org/dc/terms/description>
?description . ?relatedElement <http://localhost/score> ?score } ORDER BY DESC
(?score) LIMIT 4');
Note you can also try increasing the SPARQL query time outs in the Virtuoso
configuration file (virtuoso.ini) which would enable the query to run:
[SPARQL]
;ExternalQuerySource = 1
;ExternalXsltSource = 1
;ResultSetMaxRows = 1
;DefaultGraph = http://localhost:8891/testgraph
MaxQueryCostEstimationTime = 200 ; in seconds
MaxQueryExecutionTime = 100 ; in seconds
;ImmutableGraphs = http://localhost:8890/dataspace
;PingService = http://rpc.pingthesemanticweb.com/
;DefaultQuery = select * where { ?s ?p ?o . }
But we still need to determine why the query execution time is so long ...
Best Regards
Hugh Williams
Professional Services
OpenLink Software
Web: http://www.openlinksw.com
Support: http://support.openlinksw.com
Forums: http://boards.openlinksw.com/support
Twitter: http://twitter.com/OpenLink
On 20 Nov 2009, at 09:30, Mirko wrote:
> Hi,
> I have a SPARQL query which performes well when querying a single graph but
> "the estimated execution time exceeds the time limit of 400 (secs)" when
> querying two graphs. This is also true if the second graph is empty. Why is
> this the case / how can I fix this?
>
> Query A (performes well):
>
> SELECT ?description FROM <http://localhost/graphA> WHERE { ?recource
> <http://purl.org/dc/terms/subject> <http://localhost/someElement> .
> ?recource <http://purl.org/dc/terms/subject> ?relatedElement .
> ?relatedElement <http://purl.org/dc/terms/description> ?description .
> ?relatedElement <http://localhost/score> ?score } ORDER BY DESC (?score)
> LIMIT 4
>
> query B (times out):
>
> SELECT ?description FROM <http://localhost/graphA> FROM
> <http://localhost/graphB> WHERE { ?recource
> <http://purl.org/dc/terms/subject> <http://localhost/someElement> .
> ?recource <http://purl.org/dc/terms/subject> ?relatedElement .
> ?relatedElement <http://purl.org/dc/terms/description> ?description .
> ?relatedElement <http://localhost/score> ?score } ORDER BY DESC (?score)
> LIMIT 4
>
> -->"The estimated execution time 664 (sec) exceeds the limit of 400 (sec)."
>
> Regards,
> -Mirko
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