Question

I was doing a simple query using explain to know precisely the execution time.

    $this->db->toto->find($req)->sort(array('date' => 1))->explain();

I now want to use explain on a map and reduce query, how to do that ?
Should I use the ‘classic’ profiling system?

I’m trying to compare the execution time of theses 2 queries.

ex:

    $res = $this->db->command(array(
        "mapreduce" => "toto",
        "map" => $map,
        "reduce" => $reduce,
        "finalize" => $finalize,
        "query" => $req,
        "out" => array("inline"=>1)
    ))->explain();

Doesn’t work because command return an array (explain need a MongoCursor).

Thanks you a lot 🙂

Answer 1

Explain won’t work on a command like map/reduce. The beat you can do is run explain on the query you’re using.

If you just need execution time, you can run the m/r and time it. That’s how explain determines the execution time.