Re: [Bigdata-developers] Query projections and multiple VALUES clauses

[Michael S. <ms...@me...>]

Dear Lee,

thanks for reporting the two issues!

We have identified the problems causing the behavior (see my comment in the parent task http://jira.blazegraph.com/browse/BLZG-1141 <http://jira.blazegraph.com/browse/BLZG-1141>). A correctness fix for both issues is available in branch BLZG48and50 <https://github.com/SYSTAP/bigdata/tree/BLZG48and50>, however the fix might induce some performance regressions. We want to look at performance in more depth before merging into master (probably as part of a more exhaustive refactoring), so it might take a while until this will appear in master. 

Best,
Michael


> On 13 May 2015, at 16:06, Bryan Thompson <br...@sy...> wrote:
> 
> Lee,
> 
> Many thanks. I will assign them to Michael (Cc) to take an initial look.
> 
> Thanks,
> Bryan
> ----
> Bryan Thompson
> Chief Scientist & Founder
> SYSTAP, LLC
> 4501 Tower Road
> Greensboro, NC 27410
> br...@sy...
> http://blazegraph.com
> http://blog.bigdata.com
> http://mapgraph.io
> 
> Blazegraph™ is our ultra high-performance graph database that supports
> both RDF/SPARQL and Tinkerpop/Blueprints APIs.  MapGraph™ is our
> disruptive new technology to use GPUs to accelerate data-parallel
> graph analytics.
> 
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> 
> On Wed, May 13, 2015 at 10:03 AM, Lee Kitching <le...@sw...> wrote:
>> Hi Bryan,
>> 
>> I've raised these at http://jira.blazegraph.com/browse/BLZG-48 and
>> http://jira.blazegraph.com/browse/BLZG-50.
>> 
>> Thanks
>> 
>> On Wed, May 13, 2015 at 12:41 PM, Bryan Thompson <br...@sy...> wrote:
>>> 
>>> Lee,
>>> 
>>> These definitely look like bugs.  Can you please file tickets at
>>> http://jira.blazegraph.com and include sample data and expected
>>> solutions for each?  We will try to get the fixes into the 1.5.2
>>> release.
>>> 
>>> Thanks,
>>> Bryan
>>> ----
>>> Bryan Thompson
>>> Chief Scientist & Founder
>>> SYSTAP, LLC
>>> 4501 Tower Road
>>> Greensboro, NC 27410
>>> br...@sy...
>>> http://blazegraph.com
>>> http://blog.bigdata.com
>>> http://mapgraph.io
>>> 
>>> Blazegraph™ is our ultra high-performance graph database that supports
>>> both RDF/SPARQL and Tinkerpop/Blueprints APIs.  MapGraph™ is our
>>> disruptive new technology to use GPUs to accelerate data-parallel
>>> graph analytics.
>>> 
>>> CONFIDENTIALITY NOTICE:  This email and its contents and attachments
>>> are for the sole use of the intended recipient(s) and are confidential
>>> or proprietary to SYSTAP. Any unauthorized review, use, disclosure,
>>> dissemination or copying of this email or its contents or attachments
>>> is prohibited. If you have received this communication in error,
>>> please notify the sender by reply email and permanently delete all
>>> copies of the email and its contents and attachments.
>>> 
>>> 
>>> On Wed, May 13, 2015 at 6:51 AM, Lee Kitching <le...@sw...> wrote:
>>>> Hi,
>>>> 
>>>> We are trying to migrate our native Sesame database to Blazegraph,
>>>> however
>>>> we are encountering a problem with the following query which returns no
>>>> results in Blazegraph:
>>>> 
>>>> SELECT DISTINCT ?uri WHERE {
>>>>  {
>>>>    SELECT DISTINCT (?uri_d as ?uri) WHERE {
>>>>      VALUES ?type { <http://type1> <http://type2> <http://type3> }
>>>>      VALUES ?dg { <http://graph1> }
>>>>      GRAPH ?dg { ?uri_d a ?type . }
>>>>    }
>>>>  }
>>>>  MINUS
>>>>  {
>>>>    SELECT DISTINCT (?uri_l as ?uri) WHERE {
>>>>    VALUES ?type { <http://type1> <http://type2> <http://type3> }
>>>>    VALUES ?lg { <http://graph2> }
>>>>    GRAPH ?lg { ?uri_l a ?type . }
>>>>    }
>>>>  }
>>>> }
>>>> 
>>>> This returns a single result in Sesame since the first subquery returns
>>>> one
>>>> result and the subquery in the MINUS clause returns none. Executing the
>>>> first subquery
>>>> 
>>>> SELECT DISTINCT (?uri_d as ?uri) WHERE {
>>>>  VALUES ?type { <http://type1> <http://type2> <http://type3> }
>>>>  VALUES ?dg { <http://graph1> }
>>>>  GRAPH ?dg { ?uri_d a ?type . }
>>>> }
>>>> 
>>>> returns 0 results in Blazegraph, however moving the single graph value
>>>> into
>>>> the GRAPH clause:
>>>> 
>>>> SELECT DISTINCT (?uri_d as ?uri) WHERE {
>>>>  VALUES ?type { <http://type1> <http://type2> <http://type3> }
>>>>  GRAPH <http://graph1> { ?uri_d a ?type . }
>>>> }
>>>> 
>>>> returns the expected result. Combining the two VALUES clauses into one:
>>>> 
>>>> SELECT DISTINCT (?uri_d as ?uri) WHERE {
>>>>  VALUES (?type ?dg) { (<http://type1> <http://graph1>) (<http://type2>
>>>> <http://graph1>) (<http://type3> <http://graph1>) }
>>>>  GRAPH ?dg { ?uri_d a ?type . }
>>>> }
>>>> 
>>>> also returns the result. Does Blazegraph support multiple VALUES clauses
>>>> in
>>>> the same query? I would expect the three queries above to be equivalent
>>>> (in
>>>> the case of a single graph).
>>>> 
>>>> Another issue is that Blazegraph appears to be inconsistent when
>>>> projecting
>>>> variables from inner subqueries. The query:
>>>> 
>>>> SELECT DISTINCT (?uri_d as ?uri) WHERE {
>>>>  VALUES ?type { <http://type1> <http://type2> <http://type3> }
>>>>  GRAPH <http://graph1> { ?uri_d a ?type . }
>>>> }
>>>> 
>>>> returns the expected result, however wrapping this in another
>>>> projection:
>>>> 
>>>> SELECT ?uri WHERE {
>>>>  SELECT (?uri_d as ?uri) WHERE {
>>>>    VALUES ?type { <http://type1> <http://type2> <http://type3> }
>>>>    GRAPH <http://graph1> { ?uri_d a ?type . }
>>>>  }
>>>> }
>>>> 
>>>> causes no results to be returned. Surprisingly, projecting an unused
>>>> variable from the inner query:
>>>> 
>>>> SELECT ?uri WHERE {
>>>>  SELECT ?type (?uri_d as ?uri) WHERE {
>>>>    VALUES ?type { <http://type1> <http://type2> <http://type3> }
>>>>    GRAPH <http://graph1> { ?uri_d a ?type . }
>>>>  }
>>>> }
>>>> 
>>>> causes the result to be returned again.
>>>> 
>>>> These two issues appear to be preventing the original MINUS query from
>>>> returning the expected results. Could you confirm these behaviours are
>>>> bugs?
>>>> I tried looking on the issue tracker but couldn't find anything directly
>>>> related.
>>>> 
>>>> Thanks
>>>> 
>>>> 
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>> 
>>