Performance of BIND

[keski]

Running the CQELS engine with a query that requires a BIND drastically reduces performance. For example, the query:

CONSTRUCT { [] ?p ?o . }
WHERE {
   STREAM <http://example.org/stream> [RANGE 1s] {
      ?s ?p ?o .
   }
}

is many times faster than:

CONSTRUCT { ?bnode ?p ?o . }
WHERE {
   STREAM <http://example.org/stream> [RANGE 1s] {
      ?s ?p ?o .
   }
   BIND(BNODE() AS ?bnode)
}

In my particualr use-case the latter form introduced an extra 250-350 ms delay per result. Is there an explanation for why BIND is so slow?

Also, the first query seems to reuse the same blank node for all evaluations: is this the expected behavior?