Seeding a group call with a 64bit integer will produce unwanted results. Instead of summing on an integer field, it will concatenate strings.

Example
Collection:

{ch : "channelname", size : SizeOfFile, ....some other not relevant data}

This will work in mongo console, because size is seeded with a 32bit integer or a double
db.file.group({key :

{ch : true}

, cond :

{ch : "channelname"}

, reduce : function(doc,out)

{out.size += doc.size;}

, initial : {size : 0}})

If a driver uses a 64 bit integer, the reduce function is going to go like this (printjson output):

{ "ch" : "eph.eph.main", "size" :

{ "floatApprox" : 0 }

}

{ "ch" : "eph.eph.main", "size" : "[object Object]23810924" } { "ch" : "eph.eph.main", "size" : "[object Object]2381092418479807" } { "ch" : "eph.eph.main", "size" : "[object Object]23810924184798075661612" }

{
"ch" : "eph.eph.main",
"size" : "[object Object]238109241847980756616124350139"
}
{
"ch" : "eph.eph.main",
"size" : "[object Object]2381092418479807566161243501392645007"
}
{
"ch" : "eph.eph.main",
"size" : "[object Object]23810924184798075661612435013926450074783518"
}
{
"ch" : "eph.eph.main",
"size" : "[object Object]2381092418479807566161243501392645007478351815558296"
}
.....