Listing MongoDB collections by size

In a MongoDB shell, the db.stats() command shows you the amount of space occupied by the selected database.

> db.stats()
{
  "db" : "my-db",
  "collections" : 242,
  "dataSize" : 7167367172,
  "storageSize" : 7885074432,
   ...
  "fileSize" : 14958985216,
  "nsSizeMB" : 16,
  "ok" : 1
}

The db.collection_name.stats() command returns similar metrics for an individual collection, but there’s no convenient way to see how the overall metrics are broken down by collection.

My Solution

This javascript lists collections in descending order of size and can be executed directly in the mongo shell:

var collectionNames = db.getCollectionNames(), stats = [];
collectionNames.forEach(function (n) { stats.push(db[n].stats()); });
stats = stats.sort(function(a, b) { return b['size'] - a['size']; });
for (var c in stats) { print(stats[c]['ns'] + ": " + stats[c]['size'] + " (" + stats[c]['storageSize'] + ")"); }

Or, see the gist: mongodb_collection_sizes.js.

Example output (first metric is size, second is storageSize):

my-db.foos: 5568196496 (7455608832)
my-db.bars: 716999376 (929259520)
...
my-db.bazs: 0 (8192)