AllChunkInfo.js

// This is a simple function, which takes just two arguments:
// ns: a string representing the sharded namespace to be examined
// est: a boolean to determine whether or not to use the estimate option (recommended generally)

// It is called from the mongos like so:

// AllChunkInfo("database.collection", true);
// Currently the output is CSV, will add options for other output later

AllChunkInfo = function(ns, est){
    var chunks = db.getSiblingDB("config").chunks.find({"ns" : ns}).sort({min:1}); //this will return all chunks for the ns ordered by min
    //some counters for overall stats at the end
    var totalChunks = 0;
    var totalSize = 0;
    var totalEmpty = 0;
    print("ChunkID,Shard,ChunkSize,ObjectsInChunk"); // header row
    // iterate over all the chunks, print out info for each 
    chunks.forEach( 
        function printChunkInfo(chunk) { 

        var db1 = db.getSiblingDB(chunk.ns.split(".")[0]); // get the database we will be running the command against later
        var key = db.getSiblingDB("config").collections.findOne({_id:chunk.ns}).key; // will need this for the dataSize call
        // dataSize returns the info we need on the data, but using the estimate option to use counts is less intensive
        var dataSizeResult = db1.runCommand({datasize:chunk.ns, keyPattern:key, min:chunk.min, max:chunk.max, estimate:est});
        // printjson(dataSizeResult); // uncomment to see how long it takes to run and status           
        print(chunk._id+","+chunk.shard+","+dataSizeResult.size+","+dataSizeResult.numObjects); 
        totalSize += dataSizeResult.size;
        totalChunks++;
        if (dataSizeResult.size == 0) { totalEmpty++ }; //count empty chunks for summary
        }
    )
    print("***********Summary Chunk Information***********");
    print("Total Chunks: "+totalChunks);
    print("Average Chunk Size (bytes): "+(totalSize/totalChunks));
    print("Empty Chunks: "+totalEmpty);
    print("Average Chunk Size (non-empty): "+(totalSize/(totalChunks-totalEmpty)));
}