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

rs.secondaryOk();
db.getMongo().getDBNames().forEach(function(dbName) {
    if ("local" != dbName && "admin" != dbName && "system" != dbName /* use this to (re-)start: && dbName > "am"*/) {
        var subject = db.getSiblingDB(dbName);
        subject.getCollectionNames().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
        });
    }
});

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