MapReduce with MongoDB really, really slow (30 hours vs 20 minutes in MySQL for a equivalent database)

Question

I am doing now some data analyse tests and in the first, really simple I have got very strange results.

The idea is the following: from an internet access log (a col

Answer 1

Apparently using the group function on Aggregation Framework works well! :-)

The following Javascript code gets the 10 most visited domains with their visits in 17m17s!

db.NonFTP_Access_log.aggregate(
    { $group: {
        _id: "$domain",
        visits: { $sum: 1 }
        }},
    { $sort: { visits: -1 } },
    { $limit: 10 }
    ).result.forEach(printjson);

Anyway I still don't understand why the MapReduce alternative is so slow. I have opened the following question in the MongoDB JIRA.