Haystack Indexes are typically used to:

By default, MongoDB allows up to _____ collections.

Suppose you have a collection foo with an index created using the statement db.foo.ensureIndex({a:1, b:-1, c:1}). Which of the following queries could use the index

Asume a users collections with the following fields: "_id", "username", "password", "email". At least one of the users has registered all of the fields. If you run both this queries: 1) db.users.find({}, {password: false, email: false}); 2) db.users.find({}, {_id: false, username: true}) Would the output be the same?

What is command specifying for database path ?

Describe the output of the following mongo shell JavaScript: Object.keys(db.collection.findOne())

Which could be a use case where MongoDB is a good fit?

All the replica set members contain a copy of the oplog in the _____ collection.

Which statement best describes $allElementsTrue?

The following statement is most suitable for aggregation stage: 'Used to select fields from the collection while aggregation'.

Which is not an aggregation operation? (choose all that apply)