Hi Yury,
> I find extremely useful to execute some SPARQL queries to get familiar
> with the dataset. One of these queries is default for Virtuoso (get
> all classes), I also like this one:
> ############
> select distinct ?y WHERE
> {
> ?x ?y ?z
> }
> LIMIT 100
> ###########
> It was very surprising when I found that such a simple query will lead
> to "Virtuoso S1T00 Error SR171: Transaction timed out" on
> http://dbpedia.org/sparql . Is it possible to speed it up a little?
You are basically doing a table scan, on all of the triples in the db
to make a hash of all the unique values of P, then return the first
100. The full execution time for this type of query is larger than we
currently allow any query to run for on dbpedia.org, depending on how
many other substantial queries are running at the same time.
What you can do on any Virtuoso /sparql endpoint, is to use an ANYTIME
query, by filling in the Execution Timeout field on the form:
http://dbpedia.org/c/XQOOXC
If you click on the above link and press the "Run Query" button,
Virtuoso will collect as many unique values of P it can find in 50
seconds and then return up to a maximum of 100 results, depending on
how many unique values it collected in that time period.
Patrick
---
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