title: what is the default batchSize in pymongo?
body: <p>I am using pymongo to fetch around 2M documents in one query, each document only contains three string fields. the query is just a simple find(), without any limit() or batchSize().</p>
  
  <p>While iterating through the cursor, I noticed that the script waits for about 30~40seconds after processing around 25k documents. </p>
  
  <p>So I am wondering does mongo return all the 2M results in one batch? what is the default batchSize() in pymongo?</p>