Executing db.getMongo().setSlaveOk() allows me to run a map reduce query on a replica pair slave but the equivalent group() query does not work. Reproduced on v1.4.1 and v1.4.3.

Master:

> db.sd_boxedice_checksLoadAvrg.group(
... {
... initial:

{count: 0, running_average: 0}

,
... reduce: function(doc, out)
...

{ ... out.count++; ... out.running_average+=doc.v; ... },
... finalize: function(out)
... { ... out.average = out.running_average / out.count; ... }
... }
... );
[
{ "count" : 204931, "running_average" : 131253.02999999493, "average" : 0.6404742571889803 }
]

Slave


> db.sd_boxedice_checksLoadAvrg.group(
... {
... initial: {count: 0, running_average: 0},
... reduce: function(doc, out)
... {... out.count++;... out.running_average+=doc.v;... }

,
... finalize: function(out)
...

{ ... out.average = out.running_average / out.count; ... }

... }
... );
[

{ "count" : 1, "running_average" : NaN, "average" : NaN }

]