Mongodb – Map-Reduce on `system.profile` collection

mongodbprofiler

I have a simple collection posts with a few documents in it. I have set the profiling level to 2 allowing for profiling information to be collected into another collection system.profile. My goal is to use a mapReduce operation to collect information from the command entry grouped via various actors using this simple query:

db.system.profile.mapReduce(
    function()
    {
        emit( this.appName, this.command  );
    },
    function( key, values ) 
    {
        return JSON.stringify(values);
    },
    {
        query: {},
        out  : "command_maps"
    }
)

However, trying this in the REPL yields the following error

2021-05-10T22:09:33.494+0800 E QUERY    [js] Error: map reduce failed:{
    "ok" : 0,
    "errmsg" : "rename failed: { ok: 0.0, errmsg: \"error with source namespace: cannot write to 'test.tmp.mr.system.profile_22'\", code: 20, codeName: \"IllegalOperation\" }",
    "code" : 10076,
    "codeName" : "Location10076"
} :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
DBCollection.prototype.mapReduce@src/mongo/shell/collection.js:1145:1
@(shell):1:1

I suspect mongo is trying to temporarily write into the system.profile collection and fails due to it being readonly in a sense. Is there any way to execute this successfully ?

Unfortunately the documents are too large to add here but basically its sort of like this:

DOCUMENT

{ 
   "appName": "actor1",     
   "command": {"find": {},"ns" : "test.post""} 
}, 
{  "appName": "actor2", 
   "command": { "find": {},"ns" : "test.comments"} 
}
{
   "appName": "actor1",
   "command": { "insert": {},}
}

OUTPUT

{  appName: "actor1": command_maps: '[{command: "find"}, {command:"query"} ...]' } 
{    appName: "actor2": command_maps: '[{command: "find"}...]' }

Version: MongoDB shell version v4.4.5

PS : mapReduce is working properly on regular collections

Best Answer

So it seems special readWrite privileges are needed to execute mapReduce on system.profile collection. So I got the query to work eventually after checking through:

https://docs.mongodb.com/manual/tutorial/manage-users-and-roles/

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