Slow property graph query

[Martynas Jusevičius]

Hi,

The following (generated) query takes 1 minute to execute over a
dataset of 175862 quads in Fuseki 3.16.0. Isn't that slow?

If I remove the SAMPLE  and the last OPTIONAL, it executes immediately.

PREFIX  dct:  <http://purl.org/dc/terms/>
PREFIX  foaf: <http://xmlns.com/foaf/0.1/>
PREFIX  sioc: <http://rdfs.org/sioc/ns#>

SELECT DISTINCT  ?thing (COUNT(DISTINCT ?child) AS
?countchildd14aAdAbDbAbA) (SAMPLE(?labelthingd14aAdAbDbAbA) AS
?labelthingd14aAdAbDbAbAsample)
WHERE
  { GRAPH ?childGraph
      {   { ?child  sioc:has_parent  <https://localhost:4443/products/> }
        UNION
          { ?child  sioc:has_container  <https://localhost:4443/products/> }
        ?child  a                     ?Type
        OPTIONAL
          { ?child  dct:title  ?title }
        OPTIONAL
          { ?child  foaf:primaryTopic  ?thing }
      }
    OPTIONAL
      {   { ?thing
(((((((<http://www.w3.org/2000/01/rdf-schema#label>|<http://purl.org/dc/elements/1.1/title>)|dct:title)|foaf:name)|foaf:givenName)|foaf:familyName)|sioc:name)|<http://www.w3.org/2004/02/skos/core#prefLabel>)|sioc:content
?labelthingd14aAdAbDbAbA }
        UNION
          { GRAPH ?labelthingd14aAdAbDbAbAgraph
              { ?thing
(((((((<http://www.w3.org/2000/01/rdf-schema#label>|<http://purl.org/dc/elements/1.1/title>)|dct:title)|foaf:name)|foaf:givenName)|foaf:familyName)|sioc:name)|<http://www.w3.org/2004/02/skos/core#prefLabel>)|sioc:content
?labelthingd14aAdAbDbAbA }
          }
      }
  }
GROUP BY ?thing
ORDER BY DESC(?countchildd14aAdAbDbAbA)

Martynas