Compact all collections inside of a MongoDB database

compact.js

// This script loops though all collections of all db in a MongoDB and runs the compact operation on them
// Simply paste this into the Mongo shell

db.getMongo().setReadPref('secondary');
db.getMongo().getDBNames().forEach(function(dbName) {
    if (["local", "admin", "system", "config"].indexOf(dbName) < 0 /* && dbName > "config"*/) {
        var subject = db.getSiblingDB(dbName);
        subject.getCollectionNames()
            .filter(c => ['system.users', 'system.roles'].indexOf(c) < 0)
            .forEach(function (collectionName) {
	            print(new Date() + ': Compacting: ' + dbName + " - " + collectionName);
	            sleep(1000); // assure a cancel (CTRL-C) after "done" is executed before compact command
	            var start = Date.now();
	            subject.runCommand({ compact: collectionName });
	            var duration = Date.now() - start;
	            print(new Date() + ': done, slepping sec ' + (duration/(5*1000)));
	            sleep(duration/5); // give some time to reduce replication lag
            });
    }
});

I tried this on 4.0 with wiredTiger and it did absolutely nothing with each collection taking 0.5 secs. Any ideas?

hi @rgaufman did you run it against the primary? maybe there was not much to do - see https://docs.mongodb.com/manual/reference/command/compact/#disk-space