Sparql: COUNT(DISTINCT *) returns wrong result

Support Bug
1

Hi there,
I encountered an issue were COUNT(DISTINCT *) returns always '1' when there is only one variable in scope. Feels like a bug to me.

Stardog Version: 8.0.0

To reproduce:

  1. Load Dataset [1]
  2. Execute Query: select (count (distinct *) as ?cnt) { ?x a :A }

OUTCOME: The query returns 1
EXPECTED: The query should return 2

Sidenotes:

  1. When I explicitly count the variable '?x' I get the desired result. Query: select (count (distinct ?x) as ?cnt) { ?x a :A } -> returns 2
  2. I tested the queries with another system and it returned my expected result.

[1]: Example Dataset

PREFIX    : <http://www.test.de/count#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>

:A a owl:Class .

:i a :A .
:j a :A .
2

Thanks for the perfect bug report. I have created PLAT-4593. We will attempt to get a fix for this in the upcoming 8.0.1 release.

The only workaround I can think of in the meantime (except of using ?x, as you found) is to add memory.management=jvm to stardog.properties). Note that it will make Stardog manage intermediate query results on Java heap so one should be aware of possible OOMs on complex queries.

Thanks again,
Pavel

3

That's great to hear.

Thank you.