title: How to select all documents in MongoDB collection by parallel processes?
body: <p>I have multiple worker processes which select data from huge mongodb collection and performs some complex calculations.
  Each document from MongoDB collection should be processed only once. 
  Now I'm using following technic: I each worker marks and selects documents to process by .FindOneAndUpdate method. It finds a not marked document, marks it, and return to the worker. FindOneAndUpdate (findAndModify) is an atomic operation, so each document is selected only once.
  Selecting documents one by one looks not so efficient. Is there some way to select by 100 documents and be sure document will be processed only once?
  Is there some other, maybe MongoDB specific way to process a huge number of documents in parallel? </p>