Compact all collections inside of a MongoDB database

compact.js

// This script loops though the list of collection names in a MongoDB and runs the compact operation on them
// Simply paste this into the Mongo shell

use testDbName;
db.getCollectionNames().forEach(function (collectionName) {
    print('Compacting: ' + collectionName);
    db.runCommand({ compact: collectionName });
});

FYI if you were prepared to take your database offline, you can run a repair that performs a compaction on all collections. This article covers the two approaches and discusses a rolling update which works great on MLab hosted databases https://dzone.com/articles/managing-disk-space-mongodb

@ST-DDT which server versions do these constraints apply to? (I mean that the secondary node won't be avail for failover?)

Can you please point me to the according documentation? Thanks :)

rs.slaveOk();

for actual versions must be:
rs.secondaryOK();

anyway thanks.

db.getCollectionNames returns views too 🙃

Returns an array containing the names of all collections and views

https://www.mongodb.com/docs/manual/reference/method/db.getCollectionNames/

If you want collection names only you need something like db.getCollectionInfos({ type: 'collection' }).map(v => v.name).filter(v => v != 'system.views')