Counting all triples performance and named graphs

[Simon Bin]

Hi,

we have a data set with 500 million triples. Single named graph, fuseki
tdb2. 

We observe different performance between

select (count(*) as ?cnt) {
  ?s ?p ?o
}

~4 minutes

select (count(*) as ?cnt) {
  graph <https://data.coypu.org/> { ?s ?p ?o }
}

~3 minutes

select (count(*) as ?cnt)
from <https://data.coypu.org/> {
  ?s ?p ?o
}

takes forever and longer...? 

Especially the last case is surprising, any thoughts?