On 5/24/11 1:08 PM, Curran Kelleher wrote:
Greetings,
The problem remains, the following query doesn't execute on the public
DBPedia endpoint
<http://dbpedia.org/snorql/?query=select+distinct+%3Fproperty+where+%7B%0D%0A+++++%3Fs+%3Fproperty+%3Fo.%0D%0A%7D+limit+1>,
even with a limit:
select distinct ?property where {
?s ?property ?o.
} limit 1
Without 'distinct' it does work:
select ?property where {
?s ?property ?o.
} limit 1
Why might this be?
Because Distinct requires more work.
Shouldn't the engine be able to work this one out quickly even with
'distinct', as it needs to only traverse a single triple to compute
the result?
Really? First encounter != distinct :-)
It seems the engine is doing some unnecessary computation to do with
'distinct' and is timing out because of it.
LIMIT doesn't simply the Distinct computation. It simply limits the
resultset size.
Kingsley
Best regards,
Curran
On Tue, May 24, 2011 at 9:17 AM, Kingsley Idehen
<[email protected] <mailto:[email protected]>> wrote:
On 5/24/11 8:30 AM, Mohamed Morsey wrote:
> Hi Sarasi,
>
> I've performed that query with limit 1000, and it worked on one
of our
> local endpoints, and it ended within 3 minutes.
> So I guess that the maximum time allowed for a query on the official
> endpoint is relatively low, but the query itself is executable
with limit.
>
> Hope that helps.
>
All,
If we want to have a live DBpedia endpoint that serves the whole
world,
we have to have it configured in such a way that it forces use of
OFFSET
and LIMIT.
We are very experienced with DBMS oriented data exposed to massive
concurrent users, and this stems to periods prior to the pervasive Web
of today, thus we've configured the DBpedia SPARQL endpoint with this
experience in hand.
Once again, the DBpedia endpoint is for everyone, so we deliberately
protect against inconsiderate use e.g. attempting to get massive
results
sets in single query passes at the expense of others.
Also remember, you can make application or service specific
instances of
the DBpedia SPARQL endpoint via a number of offerings on EC2 if
you seek
hassle free reconstruction of DBpedia.
Links:
1. http://blog.dbpedia.org/2011/01/31/dbpedia-36-ami-available/ .
--
Regards,
Kingsley Idehen
President& CEO
OpenLink Software
Web: http://www.openlinksw.com
Weblog: http://www.openlinksw.com/blog/~kidehen
Twitter/Identi.ca
<http://www.openlinksw.com/blog/%7Ekidehen%0ATwitter/Identi.ca>:
kidehen
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Regards,
Kingsley Idehen
President& CEO
OpenLink Software
Web: http://www.openlinksw.com
Weblog: http://www.openlinksw.com/blog/~kidehen
Twitter/Identi.ca: kidehen
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