Re: [dotNetRDF-bugs] Problems with SPARQL query

[Rob V. <rv...@do...>]

Tom

This query hit a bug in our lazy evaluation implementation, turns out this
query is one that looks like it can be lazily evaluated but can't in
practise which causes us to do lazy evaluation anyway which is very slow
when fully evaluating a BGP

I have already fixed this to instead fall back to normal BGP evaluation
when this cases are hit and the query now completes fine.

As a workaround for previous versions you can disable lazy evaluation:

SparqlOptimiser.RemoveOptimiser(SparqlOptimiser.AlgebraOptimisers.Find(x
=> x.GetType().Equals(typeof(LazyBgpOptimiser)));

Bonus question:

FROM and FROM NAMED are only allowed by the SPARQL specification at the
top level as they set the dataset for the entire query (including
sub-queries)

Rob

On 06/01/2015 20:51, "tom...@gm..."
<tom...@gm...> wrote:

>Hi Rob
>
>I've been having some problems with a SPARQL query. Actually I extracted
>it from a larger one, where it is a subquery. As a subquery I get some
>inifinite loop and must terminate the process. On its own it times out. I
>get the same results in all version from 0.7.2 onwards.
>
>prefix hydra: <http://www.w3.org/ns/hydra/core#>
>prefix dcterms: <http://purl.org/dc/terms/>
>
>select ?member ?title
>{     
>  graph <http://localhost:17899/brochures>
>  {
>    <http://localhost:17899/brochures> hydra:member ?member .
>    ?member dcterms:title ?title
>  }    
>}    
>order by ?title
>offset 0  
>limit 10
>
>I've played with this query to identify the problem and I've got some
>results. It works fine in either one case:
>
>1. Remove order
>2. Remove limit
>3. Replace GRAPH <> with FROM <>
>4. Remove the first triple pattern
>5. Replace two triple patterns with property path (and ditch ?member)
>
>Key observation however is a modification to 3. If I use FROM <> but wrap
>the triple pattern in a BGP I'm getting timeouts all the same.
>
>My dataset can be downloaded from http://ge.tt/19Q3B582/v/0?c
>
>As a bonus question, please tell me why is is not possible to use FROM
>(NAMED) in subqueries? SPARQL specification or library limitation?
>
>Thanks,
>Tom
>
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