We have sharded setup on 2 machines and have a 120GB collection on these machines.

Ran a mapreduce job through db.runCommand with a limit attribute, to test the map-reduce functions and it did threw an error message that limit attribute is not allowed.

Specifics

db.runCommand({mapreduce: "bigdm",
map:m,
reduce: r,
limit:100,
query: { "dynamicRL" : { "$exists" : true}},
out: "dt",
verbose: true});

It gives me following error message

{
"assertion" : "don't know mr field: limit",
"assertionCode" : 10177,
"errmsg" : "db assertion failure",
"ok" : 0
}