Sarven Capadisli wrote:
> On 12-03-08 02:47 PM, Paolo Castagna wrote:
>> Rob Vesse wrote:
>>> Yes one possibility that me and Andy raised in that discussion was the
>>> use of the following:
>>>
>>> SELECT DISTINCT ?g WHERE { GRAPH ?g { } }
>>>
>>> Since GRAPH ?g is defined as an iteration over all graphs in the dataset
>>> (which may of course be modified by the presence of FROM and FROM NAMED)
>>> and the empty graph pattern returns a single empty solution (i.e. always
>>> matches) then on paper at least this query should do the same job and be
>>> much more performant. Whether this query works may vary depending on
>>> how accurately an engine actually implements the SPARQL spec because the
>>> whole dataset/GRAPH interaction is one of the areas prone to ambiguities
>>> in the spec and differences of opinion between implementers
>>
>> Indeed, the optimization might already be there... Sarven, could you
>> try to see
>> if SELECT DISTINCT ?g { GRAPH ?g { } } gives you what you want, faster?
>
> First of all, that worked! It took about 10-15 minutes the first time I
> tried it. I just ran it again.. and 30 minutes in, still waiting for a
> response. Odd.
Hi Sarven,
that is too slow for any UI interaction, I suggest you try the other approach,
you could take the opportunity to use the VoID vocabulary and/or the SPARQL 1.1
Service Description to add triples which describe your data.
This way you can make the { ?s ?p ?o } more selective and search for:
{ ?s a void:Dataset } or { ?s a sd:Dataset } or { ?s a sd:Graph }.
Have a look here:
- http://www.w3.org/TR/void/
- http://www.w3.org/TR/sparql11-service-description/
Out of curiosity, how big are your GSPO.dat and GSPO.idn files in the TDB
directory? To answer you query, TDB needs to scan through all that index.
While with { ?s a void:Dataset } will need to scan through only a small
fraction of the POSG index, I suppose.
Try and let us know,
Paolo
>
> -Sarven
